There is an excellent review of the various free and commercial Linux distributions at
http://www.desktoplinux.com/articles/AT5886901845.html
Three that I will be investigating
I know a couple of people who run Vector Linux
http://www.vectorlinux.com/ on old machines like 32MB/133Hz and it seems to work remarkably well - don't retire that old hoss yet!
Mepis Linux
http://www.mepis.org/ is free, Debian based and visually stunning - excellent reviews, liveCD so you can test it before installing it.
Xandros Desktop OS version 2
http://www.xandros.com/ is a beautiful distro and includes Codeweavers' Crossover Office and Crossover Plugin so you can run most Windows apps (IE, Media Player, Office, PhotoShop, Visio, etc) directly.
The review above is very worth reading.
Finally (non-Linux), The OpenCD
http://theopencd.sunsite.dk/ provides a good selection of free open source software for Windows. Any of the selection, particularly OpenOffice 1.1 (a full fledged M$ compatible office suite) is worth the 5 quid (GB pounds) asking price.