Bridge Command requires DirectX 7 to 9 to be installed in order to run. Pretty much any graphics card you can buy should be able to run Bridge Command, though of course the faster the better.
It may well be worth trying to re-install DirectX on your existing hardware before buying anything new - You can get DirectX9.0c from http://www.microsoft.com/downloads/details.aspx?FamilyID=2da43d38-db71-4c1b-bc6a-9b6652cd92a3&DisplayLang=en (http://www.microsoft.com/downloads/details.aspx?FamilyID=2da43d38-db71-4c1b-bc6a-9b6652cd92a3&DisplayLang=en). If this doesn't run, it may be possible to find an installer for DirectX 7, which will almost certainly run on your hardware, although I haven't been able to track down where to download it from.
