I just wiped my computer and upgraded my OS to Windows 7 from XP and thought that while I freshened it up a bit I might as well address some of the other issues with age that have been nagging me; namely the graphics card.
I do use the computer for gaming. I plan on buying Fallout Las Vegas and Sid Meier's Civ V.
I currently use an ATI Radeon X1950 series (http://www.newegg.com/Product/Product.aspx?Item=N82E168...) card. My biggest issue with the card is really its lack of support above DirectX 9. My power supply shouldn't have a problem handling anything as I have a Seasonic M12 700W power supply.
My biggest compatibility concern is my motherboard. I have an Abit (do they even still exist?) AW9D-Max (http://www.newegg.com/Product/Product.aspx?Item=N82E168...). When I bought my computer (end 2006) it was really high end... lol. The MoBo's PCI-e slots are x16 and I'm finding it really hard to find gfx cards with the newest directx support that fit that configuration (and having anything resembling decent graphics quality).
If you haven't noticed I love newegg.com as I've always had great response time from them.
I have no preference in make. I break my ATI and nVidia gear with equal abandon.
SLI or Crossfire is a possibility if that's what getting decent performance out of those old PCI-e slots takes. But I am on a budget her and I ideally would like to keep things under $200 (but am open to more expensive suggestions).
I have a bit of a budget monitor by today's standards too, but am thinking of upgrading it as well if I feel like the graphics card upgrade options will really extend the life of my computer.