chipmonk 0 Newbie Poster

Hey guys, I need a new graphics card. Not too sure which are good as I'm new to building pc's.
My PC details are as follows ;
Dell XPS 420
Intel(R) Core(TM)2 Quad CPU Q6600 @ 2.40 GHz 2.40 GHz
4.00 GB ram
32-Bit Operating system.
Nvidia Geforce 8600 GTS 256MB -- Original graphics card.
Looking for a decent Graphics card to run high PC game's for around £100-150 if possible.

Any more details required lemme know, Thanks.