I think there is a ini file in your profile folder (the one where your saved games are - usually in My Documents/C&C Generals).
In there is the game speed = 30 or something like that. The game speed is directly proportional to the FPS. So beware if you set it to 60 you wil get double the game speed.
Ah, correction. Extract the file you downloaded to your profile and override the existing one. That file removes the gamespeed and FPS relationship.