Without the info described above as to what you use it for, its hard to say]
But looking at that spec, I'd say upgrade the RAM
A 733 processor will do most things nowadays easily, but XP and 2000 Pro need 256mb to really shine
We have several 500-800mhz PC's which have upgraded to XP Pro and run successfully (with some graphic settings turned off) with us bumping the RAM up to 256mb
After that, if you have the cash, get a new graphics card, geforce 3 and 4 should become much cheaper with the new FX chip due this year