El Segundo, Calif. - Toymaker Mattel said on Wednesday that its BarbieGirls.com virtual world for kids has now surpassed 4 million registered users, within three months of its launch. This week the company will also ship the Barbie Girl, a $59 MP3 player that doubles as a fashion doll and USB key that unlocks additional content on BarbieGirls.com. Mattel also plans next week to launch Barbie Girls websites in five additional languages, including French, Spanish, Italian, German and Portuguese.