If you are looking to upgrade/purchase a new computer or you have older computers and you are ready to upgrade to Revit 2011  you should check the list of Revit supported Graphics Cards listed on the Autodesk website:

http://www.autodesk.com/us/revit/revit_graphics_hardware_-_graphics_hardware_list_final.html

If your graphics card doesn’t appear on the list it doesn’t mean it won’t work, just that it has not been tested to see if it will work with the latest software.