Hi all im new here, anyway i want to upgrade my graphics card put i cant decide on which one to pick

i was looking at these two websites as i have used them both before and my system stats are below, oh and my budget is around £200 sterling but i think i would need a new Power Supply Unit too!!
than you in advance
jon
Cheap Nvidia Graphics Cards From Ebuyer
nVidia PCI-Express Graphics Cards from CCL - Awarded Best Online Retailer 2007 & 2006
CPU: AMD AthlonX2 5200 AM2
Mainboard: Asus m2n-e am2 socket
Memory: 2gb DDR2 533 RAM
Hard Drive: 80gb Sata2 H/D
Video: geforce 7900gs 256mb sparkle
Sound: creative soundblaster audigy zs 2
CD Rom: dvd rw +/-
Power Supply: atx 550w ce active pfc dual fan Power Supply Unit
Printer: epson 5150
OS: Vista Ultimate