I wouldn't worry too much about AMD with ATI or Nvidia- they won't make much difference (though its harder to find an SLI chipset for AMDs than crossfire chipsets). As for the GTS250- it should work fine in windows 7, but you can probably get an ATI 4850 for less, or get a 5750/5770 for only a little more. The 4850 and 5750 are prety much equal in performance, though the 5750 can do DX11, which the other two can't. It will also be a little more expensive than the 4850. I don't know as much about prices in the UK, but here in the US, the 4850 is cheapest, the 5750 is generally a bit more, but closer in price to the GTS250. The 5770 is a bit more expensive, but a bit faster, and is generally the best performance for the price.