Upgrading GPU

[Crunchynut]

Current PC specs:

CPU: AMD Phenom quad core 2.2ghz

RAM: 4 GB RAM

GPU: ATI Radeon 3100 onboard graphics

PCU: 250-350 Watts I believe

http://www.foxconnchannel.com/Product/Chassis/detail_overview.aspx?id=en-us0000132
http://www.uktsupport.co.uk/advent/pc/PQD4003.htm

Both links provide sufficient information about my PC incase of compatibility issues.

Amongst other things I am looking to be playing GTA4 with relatively high settings.

Im guessing I will probably have to replace the PCU along with the GPU.

Just want to know what GPU to get to make sure its compatible and good performance. Including the PCU, Im looking at a budget of around £150 but dont hesitate to give me options that may increase performance.

It looks like im asking a lot but all help is appreciated.

 

[Crunchynut]

Thanks all, I guess ill just go with the majority on this one. Most people said the HD5770 including another forum. So, thanks for the help.

 

[Crunchynut]

Ok I see, well I think i can stretch a bit further. Regarding the power consumption on the HD6850, would I actually have to buy a new power supply to accompany it? If its recommend then I will.

 

[Crunchynut]

Perhaps I'm too lazy to do the research myself, but theres a lot of information to take in about compatibility. If I were to get the Corsair CX400 or 430 PSU and the HD6850 (XFX and Sapphire same in terms of compatibility?) would there be no issues when installing both of them inside my PC? Ive read a few articles about compatibility but its fairly confusing for someone like me. Links are at the top to some details about my PC, would be greatly appreciated.

Edit: First link works now, and I keep calling a PSU, PCU. -_-