I have a Dell 2400 running XP Home SP2.  I've tinkered with XP's built-in ZIP utility, but have not found it to be useful at all in shrinking audio or video files.  If I have a 7.5MB file, and use XP's ZIP program, it will be "shrunk" to about 7.48MB.  Whoo hoo.  I suppose this program is only useful for text documents.