Player moves different on some PCs

[Tanja]

i think i had the problem from the beginning on. (since i started to make this game and build it from the ground up)
on some computers the player moves with a good, constant speed. at other computers he moves strange, like speeding up, then slowing down. this slowing down is only a little bit, but enough to give everyone a bad feeling while playing. is is like constanly hit the brakes and let go of them...

i guess this problems occur at the computer where the heavy display errors also are. this one: http://gamedev.comdel.net/index.php?topic=1137
but they also occur at another pc, where the graphics are good.

[Jam0864]

run it in debug mode and see if the framerate changes at all.

[Tanja]

my friend who tested it at another computer, says it changes not.
here on my school computer the frame rate changed about two or three all the time.