Huh? I am using a a qx9450 clocked at 3.6Ghz, 4 GB of ram at 1066, velociraptor, and 4850 at 700/1100. My OS is Vista 64 U.
I was running the game a 1920x1200 with forced 4x AA edge detect so 12x sampling turned on. I could even be recording with FRAPS during a huge keep siege (200+ players) and STILL get 20-30 FPS. I have no clue what was your slow down problem. If you really want, when I get off work, I can find a link to the HQ video I made of a keep siege a long time back. it's something like 1.2GB in XVid encode, but I also have links to 6 separate smaller chunks.