Hmmm. Well, I'm looking at all my games through FlashFXP (I have all my games stored on my XBOX hard drive), and although most games have all their sounds in .bin files (which I have no idea how to decompress or convert), I've found that some games have music that are in PC-ready formats. I'll list what I find here:
Beyond Good & Evil - Couldn't find any.
Bruce Lee - Couldn't find any.
Burnout 3 - Uses .awd files, which I have no idea how to use.
Top Spin/NCAA College Football - Couldn't find any.
Fable - Couldn't find any.
Fatal Frame 2 - Couldn't find any.
Fight Night 2004 - Uses .bnk files. Anyone know how to use these?
Ghost Recon - Uses .xwb (?) files for sound, but uses .wmv files for video!
Gladius - Couldn't find any.
Grand Theft Auto III - .wav and .wma; The radio stations are in .wma format.
Grand Theft Auto: Vice City - .wav and .wma; The radio stations are in .wma format. I downloaded VROCK onto my computer and am listening to it right now!
Halo 2 - Couldn't find any.
Hitman: Contracts - Uses LARGE .wav files.
Jedi Knight - Couldn't find any.
Jedi Knight II - Couldn't find any.
Jet Set Radio Future - Couldn't find any.
Liesure Suit Larry - Couldn't find any.
Mafia - Couldn't find any.
Midway Arcade Treasures 2 - Couldn't find any.
Morrowind - Uses .wav files but a very confusing file system.
NBA Inside Drive 2004 - Uses .wav files!
NBA Live 2005 - Uses .asf files! Oh you KNOW I'm gonna be uploading some different shit onto my XBOX for this game!
Ninja Gaiden - Couldn't find any.
Panzer Dragoon ORTA - Uses .wav files!
Rainbow Six 3 - Couldn't find any.
Red Dead Revolver - Couldn't find any.
Shenmue II - Uses .snd files (?). Also, the snapshots are .bmp files so you can probably replace those with porn or something. :-p
SNK v. CAPCOM: SVC Chaos - Couldn't find any.
Splinter Cell - Uses .LS2 files (?).
Star Wars: Battlefront - Couldn't find any.
Star Wars: KotOR - Uses .wma files!
Star Wars: KotOR 2 - Uses .wma files!
Tenchu: Return from Darkness - Couldn't find any.
The Bard's Tale - Couldn't find any.
The Punisher - Couldn't find any.
Teenage Mutant Ninja Turtles - Couldn't find any.
Unreal II - Uses .ogg files!
Unreal Tournament - Uses .wmv files for the intro and ending movies but that's about it.
Wolfenstein - Couldn't find any.
X-Men Legends - uses a .wav file as a dummy file but that's it.