Thanks to all three of you guys for coming to my aid - and Moseph, if you or anyone else has time to go into a little more detail on the techniques you described, I'd be very interested, even if it most likely wouldn't turn out to be immediately useful.
And Yoozer, I was talking mainly about the narrower matter of isolating samples from an existing, finished recording, but I am also pretty uninformed, and very curious, regarding a lot of the broader things you mentioned. Where do good sample-packs come from? Most of the voices, drum samples, etc. on the Motif sound pretty good, for example, but most of the samples that I've used in Fruity, Acid, etc. tend to sound too fake or "thin" - lacking something I can't quite put a finger on.
Thanks again guys:D