Do they know it's...hard to hawk an all-star charity single with very few actual all-stars? Twenty years after the release of Band Aid's ''Do They Know It's Christmas?'' and just in time for the DVD release of Live Aid, Sir Bob Geldof is issuing an update of the track with a new batch of British popsters to raise funds for African famine relief (the original brought in an estimated $18 million). While the rerecording features Coldplay's Chris Martin, Dido, and Bono (revisiting his ''Well, tonight, thank God it's them instead of you''), the rest of the lineup are barely blips on the TRL radar. Robbie Williams? He's the king of pop everywhere but the U.S. The Sugababes? Jamelia? Still, the song (due Nov. 29) is expected to be a smash everywhere...except here, of course. And Geldof says the new kids delivered. ''It's like a football crowd f---ing demanding [to feed the world],'' he says. ''Not like 20 years ago, when you had quite good singing.''