comptuer software (especially where music is concerned is complicated).

any "music player" (itunes, windows media player and the like) will paly mp3s, but that is not all that they play. Each one has it's own proprietary format that requires that player, because no other player can paly that format.

If the downloaded song is a pure mp3 (not all songs you download will be mp3s, some will be other formats (different ecoding)), then it will work in both windows and on the 770 (I have 4 gigs worth that will, but use my ipod for music since it holds more than the 770 could). You won't be able to drag and drop from the player to the 770 folder, you'll have to find the folder where the mp3 itself is stored