ok this is getting out of hand, so lets find something out.
Nightmare how much are you willing to pay on a gfx card? No point us saying "Get a an ati 6000series or a nvidia gtx400series" if you can not afford it.
and for a new gfx card u will need to update the PSU - most take 500Wmin and some more.
Some friendly advice: if you do upgrade your gfx carda and PSU get about 100-200W more than u need. That way, in the future it will continue to run gfx card and the pc and will have some buffer built into it. Otherwise, if you get the minimum each time you want a new gfx card/CPU/etc you will have to upgrade the PSU again.
Also, if you can get on IRC, and ask about in #lw chan about this. Dugi,carol, ben, etc will all give advice about gfx card, cpu, etc if you can find em (they hide sometimes cus they shy) but they do really know there stuff.
As you may get a new gfx card but your CPU may bottleneck it, which would be a waste of money. However, i am not good on CPU's and bottlenecks so someone with more knowledge than me would be good, hence IRC.