Samsung SGH-D900 / Black Carbon

im still waiting for my 2gb transflash to come in the mail, but i figured id just stick a few songs on the phone to try it out. when im in the pc studio thing it makes me drag my songs into "other files." when i try to play them on the phone it says unsupported file format, what's the problem?

also how can i get them into the music folder so i can make a playlist? thanks in advance!
-steve