Hmm, thanks for the recommendations - now I have some good place to start, I think.
The killer app I've found for stitching loops etc together is Ableton Live (www.ableton.com). It is MIND-BLOWINGLY good, but it doesn't have a sample editor. There's a free demo available which allows you to use all functionality except "Save" for up to 30 minutes at a time. Definitely worth checking out.
Thanks Dennny,
Ant