20 Gigs is a lot of space, especially if your computer is not clutterd with junk programs that eat up huge chunks of hard drive. Microsoft Works, or MS Word, both of which are good word processors, are relatively small programs. You can put a zillion midi files in a single gig, lyrics take up about the same amount of space, and most MP3s only occupy a couple megs at most.
My giging laptop only has 10 gigs of space and I'm only using 3 gigs for everything--including Windows. It's just a matter of priortizing and using only programs that are intended for performing on the job. Leave all the other stuff on your desktop.
PSR-S950, TC Helicon Harmony-M, Digitech VR, Samson Q7, Sennheiser E855, Custom Console, and lots of other silly stuff!