Are you worried that the game might be too fast on some machines, or that it will be too fast on some and too slow on other machines? The first is solvable by several methods (including tweening, which Mark Sibly did a good tutorial for on the message boards, or something else like a frame-rate limiter). The second requires both a tweening-type solution as well as "throttling" of your graphics or calculations (i.e. on slower machinces you would have to use simpler graphics routines or AI calculations, etc., leading to the possibility of a different game experience on different hardware, even though you have the same game speeds), which is much harder to do.