Vista - media center audio/video playback "glitches"

I am an OEM system developer working on a configuration for a new Windows
Video Media Center based HTPC. I have experimented with a few motherboards
for the new HTPC product that I'm working on, but felt that the Intel DP35DP
was well suited for the system I'm building, due to it's design/features. I
have also seen other HTPC companies that have based products on this
motherboard. That being said...

The system I have built has audio/video "glitches" (pauses for a 10 ms or
so, every few seconds) during playback, and I don't seem to be able to
isolate what's causing it.

Note that I have already tried swapping out the CPU, memory, and hard drive.
I have verified that all motherboard drivers are the latest ones from the
Intel web site, and I downloaded the latest Nvidia driver from their web
site. I have also updated the motherboard to the latest version of the
BIOS.

The system configuration is as follows:
- Intel DP35DP motherboard (with onboard HD audio)
- Intel Dual Core 4400 processor
- 1 GB of PC2-6400 (800 mhz DDR2) memory (2 - 512 MB modules)
- Nvidia GeForce 8500GT video card
- 300 GB Seagate SATA drive

Anyone have any ideas what might be causing the problem???