Plenty of stars joined the geeks this week at E3, the annual videogaming expo in Los Angeles. James Cameron divulged details about his upcoming 3-D movie and game, Avatar, while Steven Spielberg vouched for Microsoft’s revolutionary motion-capture sensor code-named Project Natal. But the biggest celebs were Paul McCartney and Ringo Starr, who unveiled The Beatles: Rock Band, which allows up to six people to jam — with guitars and drums — to 45 of the group’s songs (including ”Day Tripper” and ”Here Comes the Sun”). ”Who’d have thought we’d end up as androids?” joked McCartney. Cameron would point out, no doubt, that ”avatar” is the proper gaming term.