I think he means 1GB of memory.
A 512 anything that is current will handle FSOpen and the MediaVPs pretty fine. A 1 GB card is nothing to sneeze at, but not necessary for full enjoyment. And while SLI/Crossfire of 2 512=Teh Win and 2 1024's=Teh Awesome, also not necessary.
Recommendation would be any card that honestly (and FULLY) supports Shader Model 3.0. As long as you keep that spec in mind and aim for at least 512 mb of memory, you will not go wrong.
And that ATI link thread is for much older radeons, though it may prove useful for the current x1900 you currently have.