DVD playback is jerky in Vista Home Premium

I've seen a few posts here that are similar and one that sounds almost
identical.
JR did such agood job in his description of the problem, I'll quote him:

"I have a problem on released Windows Vista Media Center. On some DVDs
(not all), playing back a DVD causes the video to jerk every 1/2 second
or so. It is very repetitive and consistent. Audio is always fine.
It's the video. It looks like it slows down, speeds up, slows down,
speeds up, etc. All within this 1/2 second to 1 second period."

I have a M7780n Media Center PC. I've recently updated both the bios and
video driver to the latest versions posted on the HP site to address a
problem of the display not responding when resuming power from sleep mode.

It may be coincidence, but since I have noticed this problem playing DVD's
with Media Center.

I don't have this problem playing the same DVD with Windows Media Player or
with HP's HD DVD Play.

Now here's the kicker, I only have the playback problem in Media Center
iwhen it's in full screen mode!
If I reduce it to a window. the playback is normal.

I checked my CPU usage during playback in Media Center, and it's in the
15%-35% range.