Windows 7 - Trouble with VOB playback in RC, not in beta?

Windows 7 beta in media center played VOB files flawslessly. Once I installed Windows 7 RC, I get jumpy and freezing play on about 75% of what I try to play. Those same files will play with no problem in Media Player. I'm running this on a machine that I've added nothing to (codecs, transcoding, etc.). Just curious if anyone has experienced the cahnge in playback from the beta to the RC. I've even tried updating the video drivers, but the card is old enough that the only drivers are the ones shipped with Windows 7. Any ideas?

need a bit more info - system specs, was it a clean install, what video card are you running, etc.

This is an extra work computer that has been used for CAD. Using it to test Windows 7.
Pentium D 2.8 Ghz, 3 GB memory

Video card is Radeon X300 SE

It was a clean install both for beta and RC (running build 7100)

The curious thing was it worked fine on the beta run, but the RC build is where the Media Center video is so jumpy. You can turn around and start the same movie that gives problems in Media Center, but run it in Windows Media Player and it runs without any problems. Again, no extra codecs added to this system.