Video playback problem

[mandelbrot_set]

Annoying thing keeps happening to me. When I am playing a movie sometimes suddenly both audio and video jumps forward like one second;
it seems like that computer just forgets to play a few frames; sometimes it happens three times during a movie, sometimes it doesn't happen at all.
I'm using BSPlayer 1.22.817 and ffdshow filter right now, but the same thing happens with older versions of BSP. I have also tried different versions of
ffdshow and XviD codec and even a different player (Core Media Player), it did't help. I've reinstalled my Windows and I've tried many drivers for
my video and sound card and even motherboard, nothing helps.
My computer: Atholon XP 1700+, Radeon 9000Pro, SBLive, Via KT333 based MB,
Win 2K Service Pack 4
The CPU load during playback is around 30%
Can anyone help me with this problem.

[enjoialone]

dunno if this will help but, run dxdiag and go to the sound tab, and move the sound acceleration bar to basic acelaration