I am running XP FYI. I find it really hard to believe that your card does not support this monitor. I would just try as many things as possible as it is a really good monitor. If you game, an 8800GTX or better should be in your future. Also you might want to try to contact XFX support, they may have some insight.
I was using XP when I first had this problem and I wanted to switch to vista anyhow so I did. It is a very strange problem and I have not found much info on it.
I'm trying my best to make it work as I just found out looking at the receipt that they charged me about $120 less. I bought it for $350 including tax at circuit city.