Holly cow, 285gb memory?, actually Windows Vista Home Premium comes with DirecX 10 already, but what it may be making it slow might be the video card, when I got my computer it was running FPSC at 16 fps, then upgraded the video card to a ATI Radeon 3650 and the fps rate jumped to 38 to 40. You should also be running FPSC under Windows XP SP2 Compatibility. That would help a lot.
I am running Windows Vista Home premium SP2, 1GB memory, dual core 2.8 GHz each, without any mods. Even if I use fraps, it drops to like 20 frames per second.
if you wanna know exactly what your computer is running you can go to start menu and type in search, dxdiag , and you will get a complete report of your directx and more stuff.
...........(o o)........
--oooO--(_)--Oooo---