I throw out all the ones that are too slow. Right now I'm getting ready to retire my Pentium 3, which is a very stable file server and going to move my P4 into it. And may end up getting a dual core board/cpu soon after and taking the P4 out. I also have a P233mmx system for legacy gaming with a 4mb monster 3d 3dfx video card in it, but I rarely ever use it. The games are too outdated in graphics to play and leave very little nostalgic value. I also built up one of my P4 with 6600GT agp and monster 3d II voodoo2 video card in it but it is just sitting idle without a hard drive.
Realistically anything that isn't core2duo or above is pretty crummy for gaming on, all of my friends wonder why I have more than my two core2duo computers. Playing battlefield 2 for example on a pentium 4 HT is sad, very sad.. my biggest complaint about high priced video cards too. I had a ti4600 in that system for a while and although 6600gt is faster, it is pretty pathetic.