I think it also depends on how far you want to go. Maybe you should get one of those portable digital recorders? There are threads here about those, like the Zoom - they have built in microphones so you can record rehearsals, acoustic instruments, etc., but you can also plug things in and record direct, and some allow you to multitrack as far as I know. If you just want a sketchpad to catch ideas then that might make more sense than going for a computer-based system. Search for Zoom (one of the brands)...