Graphics card purchase help

I am looking to upgrade my Graphics card, currently a 7050 Geforce onboard with 128mb memory. I only wish to play RTS games and was hoping to play medievil total war 2 with higher unit count and high graphics, currently i can play medium/low settings with a medium unit size maxes out performance around the 2000 soldier mark. i would also like to try a few games like world in conflict, company of heroes etc. now my question; i was gonna get a 9800GT (cheaper deal than if i get an 8800GT) but because my computer was a pre-built it has a low PSU, 250W max, so i need to upgrade that aswell if i am getting the 9800GT.. is it worth my time seeing i am only looking to play RTS games? it will also set me back money wise and could take a month to get the money together so is there any cheaper alternatives that i could get sooner and will play the games fine no problems?

The rest of my computer specs are :

Intel 2 Quad Q6600 @ 2.33GHz

3GB RAM

Vista (x32)

You will need a new power supply for sure.

That card should be fine for most RTS games. I'm playing DOW II on an 8800 at max setting on a large monitor so you should be fine.

ooo the powersupply i s ab ig concern....u would even have a hard time running a 4670 or 9500gt...LibertySaint

Corsair 400W CX PSU - 12cm DBB Fan 80%Plus Certified Efficiency 6x SATA 1x PCI-E

Zotac 9800GT Synergy Edition 512MB DDR3 Dual DVI TV Out PhysX and Cuda ready PCI-E Graphics Card

Total: £135.35

Corsair 400W CX PSU - 12cm DBB Fan 80%Plus Certified Efficiency 6x SATA 1x PCI-E

Zotac 9800GT Synergy Edition 512MB DDR3 Dual DVI TV Out PhysX and Cuda ready PCI-E Graphics Card

Total: £135.35

anyone? would the likes of a 8600GT make much difference from what i have?

8600gt would be a fair step up, but how about a 9600gt. It can be had for about £60-£70 and can play any game maxed out (no AA). Or if you want really good bang for buck get a 4670. That may even work on your current power supply and requires no additional power connector. It can be had for as low as £50. Plays most games on high/max. Shop around.