usualy when you change gpu's the game on startup will detect the new card and optimze it but don't wait for newer drivers to be released since there are already drivers on the site,get those,then upgrade to the newest ones when they are released.you don't need to reinstall windows just some games require you to uninstall the game before you change drivers(even video cards)then reinstall the game after you install the drivers for that particular card,from what i've seen nvidia cards work on praticaly every game,ati usualy have more problems but they have gotten better.