AMD 1600+XP, 512MB 133Mhz,FX5200 128MB,80GB diamond max 9ide.
It doesnt play bad at all on this unless i play with several hard a.i.s so if thats all you play it wont be a problem its if you want to play newer fps games you get bother.
I personally would wait a while, thats what im doing, cashing in on my 18th birthday my base unit is costin £500ish at the monent but it changes. these are the specs to illustrate what you can get for not all thamuch more.
AMD 64 3200 venice, 1Gb PC3200, 160Gb sata diamondmax 10, MSI nforce 4 PCI-E mobo, new case with 400W PSU, lite-on cd-rw drive, and probably an X800 GFX card at the moment but i could spend for ever lookin for a gfx card and not pick one.
And that is more expensive than my original layout i had planned which only came in at just over 400 as you see you can get a new pc for not that much money if you shop around: try overclockers.co.uk to find the best parts as they only sell the best usually and they will sometimes be the cheapest but microdirect is a little cheaper but a poorer selection of components.
I looked at upgrading my pc and it worked out more expensive in the long run so i decided to wait a while and got a new pc that is not just better as a whole but was more "futureproof" and easier to upgrade in the future.
Thats my opinion you may be really wanting just a better pc to potter about with and play the odd game so the full new pc might not be for you but if you build a new one it means you get a new cheapy monitor and you have a second old pc for browsing the internet and word processinf and the like.