Well, I\'m not a win user, but I don\'t want to convince you of linux here (well actually I want but...however)
On Windows you should make sure that you have recent drivers installed for your card some of those drivers allow you to change between OpenGL, and normal mode for win (don\'t know if that has any influence on the game).
Furthermore all unnecessary toys should be deactivated, especially on XP just let run the most necessary things like virus scanner and firewall.
If it doesn\'t work try to shut your computer down, switch your computer off and on again (no ctrl-alt-del or restart).