Download a linux distribution cd, such as ubuntu, kubuntu, mandriva, suse, or knoppix. Put the cd in, change your bios to boot from cd, and reboot your machine. Run the installator (it should give you some sort of menu), and follow the instructions on screen. It may or may not work, since some old hardware doesn't have linux drivers. Try the different distros to see which one works/is best. If you have any questions, just post them here.