shaky DVD playing in Windows XP

I've got a Dell Optiplex GX620. 3.2Ghz Pentium D, 4GB DDR2, 256MB video card, Windows XP fully updated.

When I play a DVD its shaky, it seems to be the audio more than the video. I ran a Linux liveCD and DVD's played fine, so its not the hardware.

I've installed K-lite codecs. I've tried Windows Media player 9 and 11. I tried VLC media player with the various video output settings. I tried Windows media player classic.

 

You can understand what someone is saying but there are tiny interuptions in the audio about 3 per second. The video is almost ok, but it seems a little jittery.

I haven't tried other codecs.

 

Its a PCI express ATI card.

 

I uninstalled K-lite, installed CCCP and played a DVD in Windows Media Player Home Cinema. It worked the first time. Then I ejected the DVD and put it back in. This second time (and third, fourth) the original problem is back. fyi- the audio interupts about 5 times per second not 3 as I had stated above.

 

I've tried two different commercial DVD movies.