For technical help a little more information would be useful. That is to say what is your computer like (technical specs, operating system - 98, ME, 2000, XP - what you are doing with Desktop X - full themes, objects, widgets - and what type of games are you playing - full screen 3D games, web games, Java based games, etc.).
I can't help out your specific problem, but I can say that it is a good idea to turn off anything that isn't necessary like Desktop X when playing modern 3D games. I always turn off Desktop X, Object Dock Plus, and anything else I may be running when I play a game. Unless your system is a real monster, games will play better without those unnecessary things running.