Let's see. I can dump 1.3 GBs of emulators, 62 MBs of manga, 135 Mb of miscellaneous downloads from MSN/AIM, and 18 GB of music. I dunno is 20 GB will be enough to run PS... I should be able to wipe out some programs, too, that I don't use. Like all that CRAP that came with my printer.
Once I get it to open again, I have to shrink the number of brushes I load at the default.