Sorry I'm a bit late to the party Monsieur...
I bought a new graphics card recently and found the benchmarking data site that Nostromo recommended very helpful:
http://www.videocardbenchmark.net/gpu_list.php
Basically Monsieur, pretty much anything is better than what you have now. You can pick up something that was pretty hot stuff a couple of years ago, for a budget price now.
At the £60 price point, you can get an NVidia GT430. This will play your older games very well, but will struggle with recent top-notch graphics games.
I went for a £100 NVidia GTS 450 which can support DirectX-11, and I'm very satisfied with it, even if I can't play at maxed-out settings and top resolutions in every case.
A few other points Monsieur...
Any half-decent new videocard will need to be powered via a cable from the PC power supply, so look inside your case (after switching your PC off at the mains plug) and check whether your existing card already has one plugged in, or if there's a free one dangling from the spaghetti coming out of the power supply. The plug will be a tiny, flat (probably white) lozenge with 6 or 8 (can't remember offhand) holes in it.
As Wessie mentioned, you should also look into getting some more memory. You have a good processor, but it's a bit strangled, and memory is a cost-effective upgrade.
As you have a multicore processor, your motherboard is likely to have PCIe slots for the videocard, and use DDR2 DIMM memory. Memory should be installed in matching sets (i.e. all sticks same capacity)
The inside workings of a PC can be a bit intimidating, but it's basically Lego, and it's all a learning experience.
Let us know how you get on and if you have any more queries. I've done more fettling of my PC than my GS (which actually isn't saying much), and have the soot-streaked face and singed eyebrows to prove it.