Slashdot has an interesting blurb on running Windows 2000 on old, crappy machines. The original information is very helpful for getting rid of any performance-draining services & effects. BlackViper is also a resource for stripping OS settings down to the bare minimum for optional performance.

One big reason for running Windows 2000 on old hardware is so you can make use of otherwise "junk" boxes. Use them as file servers, web servers, test machines, internet terminals, etc.