When Venus Williams thinks of Wimbledon, what image comes to mind? She has won the tournament three times, so I expect her to name some crucial break-point or royal curtsey. Instead she rocks back, all 6ft 1in of her, and tells a story about her mother hobbling through Wimbledon village on an undiagnosed broken foot heading for the cookie tray. "Just always at the cookies!" Venus screams with laughter. Poor Mrs Williams subsequently spent time in a wheelchair having her sugar addiction mocked by her daughters. "I lost, Serena lost, but we had fun," says Venus.

We are sitting in her Paris hotel looking ahead to Wimbledon. It is perhaps 14ºC, which to Williams is like Siberian permafrost. After finding me, she hurries me with great courtesy from the hotel's door into the warm lounge.

I'm here to question her motivation. The word in tennis circles is that Venus and her sister Serena don't care any more. Having dominated the women's game, they now seldom even show up on tour. They nurse injuries, write books, appear on their reality television show, study fashion and so on. But people expect them to be mono-maniac.

At least they still like Wimbledon. Every women's final in south-west London this century has featured one or both Williams sisters. Last year Venus won. However, it was her only Grand Slam victory in the past five years. Is tennis losing the Williamses? This line of attack is fine, says her agent beforehand, but I mustn't ask about Serena. The sisters - Venus is the elder by 15 months - dislike always being asked about each other or about their family.

They were born to tennis. Richard Williams has even claimed that he gave life to his last two daughters in order to turn them into tennis champions. But Venus dismisses the notion that he was a single-minded "tennis Dad". She cites some of his exhortations:

"You want to be the most polite person in the world."

"Let's go to the park!"

"Have a life after tennis."

Yet she was being courted by sponsors at six, turned pro at 14, and at 16 made her first foreign trip to play the French Open here in Paris. What does she remember? "I remember thinking how small the cars were, just being green and wide-eyed and - not getting past the second round. Aaaaah." A big laugh.

If that 16-year-old could've seen herself now - 26 years old today (happy birthday, Venus) and world famous - what would she have thought? "She'd have been very competitive with me and she'd have thought that she could beat me." Even at 16? "I thought I was the best. That's how I was raised."

Has Venus ever faced anyone with more talent? There is a pause, an "errm", and a laugh. Then: "I don't want to get involved in being boastful or anything. I think Irina Spîrlea was really talented . . . " Spîrlea is a surprising mention. The Romanian was briefly a contender but is now remembered chiefly for having bumped into Williams during a change of ends in 1997.

But doesn't Williams sometimes lose to better players? "There've been a few times where I've gotten beat, a couple of times against Serena, a couple of times where it's just random players, where they came out and they're unbelievable, and I could not touch 'em. But usually when I lose I really beat myself, and I made 50 errors and the other person just kind of showed up and that was all anyone had to do that day, could have been sewing in the stands.

"A lot of times it's hard for my opponent to play better than me, or to serve better than me, or move better, or improvise better, because - I don't know why, just because!" She laughs. "A lot of great players out there at the moment, though."

The Williams sisters famously don't befriend colleagues. Does Venus not consider the Sony Ericsson WTA Tour a place for friendships? "First and foremost, I'm here for the tennis. Plus, I have Serena. I've never needed much more. I already had a friend on tour."

It will be clear by this point that the aim of not mentioning Serena has failed. That is Venus's fault. In an hour and a quarter of interview, I count 18 unprompted mentions of Serena, nine of their parents, and four more of the family. Meanwhile the only non-Williamses to get name-checks are Spîrlea, Lindsay Davenport and Pete Sampras, once each, and always as tennis players rather than people.

In fact, Venus and Serena areso close that recently they've often been injured together. Venus, who this year discovered that she is "an over-achiever type personality", has used the time off to study fashion design in Fort Lauderdale, Florida. "I was still trying to train and do my rehab and my school's about an hour away from my house, so it's a drive. I'm not planning on taking more classes but the thing is: my punishment if I don't play the way I should is to take a class" - gales of laughter - "because it's just such hard work."

In class, doesn't everyone think, "Wow, that's Venus Williams"?

"Oh, everyone's so stressed out and working so hard and trying to make their game look good, I mean get their classes done, that they don't really care who's there. Like last fall we had two hurricanes. School was closed, there was no extra time to make it up, and it was just crazy. I'm grateful for my day job."

As we discuss the course, suddenly there's Serena again: "We had to do sewing. Serena was good at putting zippers on" - an explosive laugh - "so I'd pass it to her. I'm really meticulous and I work a lot slower but it comes out right and when she would do her patterns they wouldn't come out right because she was going too fast, and when it came to sewing the garment I'd have to fix it."

Have she and Serena always been so close? "Yeah. We were sometimes even in the same class growing up. Whatever it was, whatever she needed, that's what I was and I am. It makes me really proud and happy if I can be something for her. Even the little things, like, 'Oh Venus, do you have a hairband?' Like if I can give her a hairband I'm so happy. I know this sounds weird. Even when I was really little and she was still in a stroller, I was pushing her around."

How to picture the scene: a giant two-year-old pushing a giant baby through the ghetto of Compton outside Los Angeles? "I just see two little girls who were just starting out in the world, and they were happy together. And they're still happy together. They've got each other. Till the end."

Naturally Serena inspired her in last year's Wimbledon final. "I was thinking, 'I want to be just like Serena', because she had played in the Australian Open final, and she was down, and she came back and won. So afterwards I told her, 'Just all I want to do is be like you!'"

In the past Serena wanted to be like her, Venus adds. "We weren't really different until the last maybe five years, because she always did what I did." Venus pauses to reflect, then says: "It's actually still the same."

Serena's studying fashion too, I point out.

"Yeah, she's doing fashion as well. Like I'll change my style, and then I'll notice she'll change her style. Or I'll start going to Miami, and she'll start going. I realise whatever I do needs to be a good example, because she's going to do it!" So Venus isn't a role model to unseen millions of children, she's a role model to . . .

"Serena, yeah! She wants to be like me! Mmmmm. Or like" - pause for long guffaw - "we'll be in a store, she does this crazy thing, if I like reach out for something, she'll reach out for it too. And then I have to like, reach out, fake it and then . . . " Venus mimes reaching for another item instead. She cracks up.

Ahem, back to tennis. Does it make her happy? She punches her fist in the air: "Oh, absolutely. Even when I lose. Like someone would ask me, 'How's it going this year?' 'Well I only played one match and I lost it.' Laugh. Because it's not that serious. You can't take it into a life-and-death experience. I don't want to look back and say, 'I was way too serious and unable to enjoy the moment and now I don't have those moments.' "

Does winning tournaments become less sweet with repetition? "Not at all. Nice! Every single time! I promise you."

Yet she doesn't aspire to establish a hegemony in tennis? "I just see this life as - what word am I looking for? - kind of just temporary. Because you know, most people - a lot of people believe in afterlife, or going to heaven, or things like that. I see this life as not necessarily the true life. There'll be something better coming next, so there'll be a time when records don't really matter." For a Jehovah's witness, Venus isn't much of a proselytiser.

She'll win Wimbledon this year, won't she? "Yeah! You said it!" she thrusts two triumphant fingers towards me. "Hahaha. I'd love to."

And after the final comes the Champions' ball. Venus will arrive in London prepared. "We really believe in what we're doing, and so we always bring a dress for the ball. Last year I didn't, I just couldn't be bothered, but normally always."

Which dress will get the nod this year? "Probably 'Old Faithful'. This Cerruti dress I pull out for charities. There's two of them I have. They're about five years old. It's good to know I still fit my dresses. Actually one of them had to get retired, it's just been photographed way too much! And the other one's in semi-retirement."

Tennis romances often start at these balls. But not for Venus? "That's always been Serena and I's rule number one, we just don't date colleagues. Just not. Just don't do it."