In general extensions to the name like LE, SE and GT can tell you a lot about the quality of a graphics card. Two cards with the same name might have very different features.
If you try and get a card with GT or GTX (not so much GS) from nVidia you'd be doing better. I myself use the 7600GT that vehelpfulguy mentions. It runs most games with no problems on full graphics. The difference between ATI and NVidia isn't too much to be concerned about.
If you are looking to get a GOOD graphics card, then you will want to buy a Direct X 10 compatible card, that will get the most out of games and the new windows vista. At the moment the main card in this catagory is the nVidia GeForce 8800 that can be seen at www.overclockers.co.uk on the front page. You'll be unlikely to get a PC from dell or hp with something like this in, I suggest a custom pc site like www.pcspecialist.co.uk which I have used myself and are great. Though I advise paying the �50 to get it delivered in days not weeks!