Mattel is using technology to create a new twist on a 48-year-old toy to appeal to today’s Web- and multimedia-savvy girls. On Thursday, Mattel unveiled Barbie Girls, four-and-a-half-inch tall MP3 players designed to look like dolls. The company hopes the new toy, which brings together Web surfing, shopping and music downloads, will cool demand for rival MGA Entertainment’s sassy Bratz dolls–a line of big-headed, skinny dolls with scant, trendy clothing.