ATI card numbers don't make a whole lot of sense. Fact is, they're not supposed to. The 5450 is a weak 64 bit memory access card, mostly for home theater work. Here's one from Newegg; http://www.newegg.com/Product/Product.aspx?Item=N82E16814102877 it's $41.00 USD. So, the 4830 is way more potent than that So, you're supposed to think the higher number is better, but in this case, all it means is the card has DX11, which would be for Windows 7. I think the 4830 is DX-10, and that goes with Vista. Yes, they're all backwards compatible with the DX-9 of XP. I'm not exactly sure which card to steer you toward, but our other members might know a bit more. Save for the wicked battle I had last night with "Maven" in "Scrabble", I'm not really much of a gamer.