I had a similar problem, used to play GR a lot then stopped - came back and couldn't get it to work. I have XP and GF4 4800se. After a lot of mucking about uninstalling etc etc I remembered I had installed a NEWER !! nvidia driver. So I went back to 4.1.0.9 and bingo all is well again. Very strange. A similar thing happened with my GF2 Ti 200 - newer driver - awful frame rate.
Moral of the story - don't install a new video driver unless you have to. If it ain't broke, don't fix it.
Can't see the point of installing Direct X9 as someone suggested. If the game isn't a DX9 and t