I installed OpenBSD 4.9 on my SparcStation 10 yesterday took awhile but X11 worked nicely on my TGX framebuffer with FVWM as the default WM which is pretty decent and unlike NetBSD thier pkg_add system is smart enough to know where to download from. I look forward to compiling software at the amazing speed of 2x50Mhz!
For old hardware NetBSD is the trick... and it seems to have enough convienience and good defaults to make using it on a server fun/safe/easy or what have you.
I have fun with running my little lisp programs on these old computers its quite fun. (I'm no lisp hacker yet.. but I can do a few simple things)