[TM2 Stadium] video freezing

[HellBear]

hi all, i been having small video freezing and idk what else to do, this happen in multiplayer and in solo, in solo is really really small the time of the freezing, but is annoying because i can see that the gameplay is not smooth

in multiplayer they can be as big as half second

this even happen with all in the video settings in the lowest posible
my video settings
no hd

i have an ati hd4850 512mb using the latest drivers, c2d 6400, xp
the fps goes between 70 and 130
fullscreen mode, using the native resolution of my screen, 1680x1050
no extra proccess in the background, only steam

plz help