A little sibling rivalry can be a good thing--just ask sisters Serena and Venus Williams. They say playing against each other has sharpened their game. They sure looked sharp on February 28, when they became the first sister act to win World Tennis Association titles in the same week. Serena, 17, won her title in Paris, France. A few hours later in Oklahoma City, Oklahoma, Venus, 18, won a tournament too. "This is just unreal," said proud pop Richard Williams. "To have them both win brought tears to my eyes."