Some of its from Planetscape Torment (another game.)
not sure where the other ones are from since its not credited by the song.
All (i think all, at least most) is made using midi sequencing.
Basically you program all the notes and various controllers into a software or hardware sequencer, then assign software or hardware synthesizers to the various parts, run the resulting signal through any processers/effects and record the output.
heh, midi sequencing in one sentence.
-TV