I am having the same problem with a Deminsion 8400.  I used the Windows XP Video Decoder Checkup Utility that you can download from Microsoft.  It was somewhat useful in the sense that it allowed me to view and select my Sonic MPEG Video Decoder Version 2.5.4.1044 over version 5.0.0.1.  That allowed me to video and hear sound for 1 minute before the audio and video would freeze in my media center.  I am guessing I'll need to find the correct mpeg-2 decoder for my TVT1 video card.   Please let me know what the resolution is if anyone finds it.  Thanks.