I've been cleaning out the 'computer closet' today. I've been saving up towers that are good enough to use, but not good enough to put back into user's hands. They are all XP or Vista towers, a mixture of last gen Pentium or core-2 duo's. I've got about 6-8 now that I get to take home and reformat! With Ubuntu or some other Linux dist... or even if I bought a Win 7 key. Nothing fast or anything, mostly 80GB drives with 1 GB ram. But good enough for school age kids and some older family members.
I'll have a trunk full of towers! ....which will probably take me 8 months to actually do anything with....
Or, maybe a Beowulf Cluster??