I reformatted the hard drive and installed linux on it.
I have a little garden of linux boxes that I use for a number of things but it keeps those old drives spinning and the power company happy. My oldest system in my little garden is 486DX with 4 mb of memory running RH6. The last addition to the garden was a P4 with 1.2 gig of memory and two 160 gb hdd and a 128mb vid card. It really screams.