Mpeg4 issues in HTPC

[trshaw]

New to the forum and looking for some advice. first the specs:

Intel P4 630 Prescot 3.0GHz OCd to around 3.5Ghz
Hyperthreading enabled
4GB DDR2 800
Asus P5LD2
MSI 8600GT 512 (Factory OC)
LG GGC-H20L Blu-Ray/HDDVD drive (LOVE THE DRIVE!!!)
Samsung-46" 1080p Flat-Panel LCD HDTV-LN-T4661F

Vista 32 running SP1
PowerDVD7.3 most recent update (even added the H.264 addon)
Currently I am running DVI-DVI for HTPC to TV

settings are set at 1080p and seems to work fine
audio is on board though SPDIF to audio amp, everything sounds fine.

Here is my issue, I can play VC-1 disks (I am Legend in Blu-Ray, 300 HD-DVD)
but have issues playing MPEG4 (Live free die hard in blu-ray, Transformers HD-DVD).

The Mpeg 4 will play for a few minutes (5-10) before the picture goes wacky, turns turns gray and is impossible to watch, kind of like a scrambled tv station (stopping and restarting does not seem to help). Audio is fine, video problem does not seem to matter if its is Blu-Ray or HD-DVD.

Would it help to switch to a DVi-HDMI setup?
Is the CPU/GPU the issues and cable not going to help?
Is is a software issue (PowerDVD 7.3 Ultra)?

or is it something im missing...I've seen this covered in other posts, but most are 3 months old and issues/hardware slightly different.

any recommendations/suggestions would be appreciated...