I'm looking at an GEForce 8600 GT card which does support Open GL 2.0 and Direct X 10. Its reasonably expensive at £100 but the cheaper 8500s also support Open GL2 not everyone mentions OpenGL on their sites but you can normally track down if it is supported.

I found an interesting link here about Vista and OpenGL. Windows Vista and OpenGL-the Facts
http://www.opengl.org/pipeline/article/vol003_9/

Open GL is mostly used for graphics and CAD applications such as Carrara, DirectX is biased towards games but also used for some of the game development toolkits and other utilities e.g, http://developer.nvidia.com/object/fx_composer_home.html