i would use slackware for that hardware. simple install and runs fast . i would install slack-get which is much like debians apt-get.

slackware 10.2 will do you just fine for that older hardware. Debian would also probably do ok . Are you strickly running CLI or a GUI ? if running a GUI run fluxbox a very light resource x manager.

I would also make sure you don't have any deamon runnings that you don't need. good luck . if you have any questions feel free to ask.