Applications that attempt to adjust their behaviour based upon the measured CPU speed (e.g. video games like Unreal Tournament) may behave erratically on lap-tops that use CPU speed stepping to save battery power. You can turn off speed stepping under XP by going to the Power control panel and selecting the Home Office/Desk power configuration. I'm not sure how people figured this out -- the control panel does not offer any clues as to what system parameters are adjusted for each setting and the Microsoft documentation is no help either. It works, though.