Video to slow compared to sound.

[Screek]

Hello there.

i just bought a new computer
specs: asus p6t motherbord - I7 920 cpu, radeon 5870, and the sound is from the motherbord.

Im getting just a bit of sound "lag" in the way of the sounds stop for like 1/4 a sec every 4-5 sec when i watch something in VLC, i dont got any problems with music only.
i have tested this by syncing up the same video on 2 machines, where mine falls behind in frames, its like my video is running 2% slower or something like that, and therefor the sound is stopping for be synced with the video.

btw i got the latest driver for everything as its brand new and just installed it all.

anyway i can fix this?

thanksin advance.