Hey Mark;
I too have a HTPC built which I use with my projector. Most of your stuff is up to snuff. It will play HD DVD via WM9 very well. Your setup is pretty much like mine. P4 3.0Ghz, ATI IGP 9100 chipset. My only suggestion is to pass on the Audigy 2 and go with the M-Audio Revolution 7.1
http://www.m-audio.com/products/en_us/Revolution71-main.html
The Audigy does some pre-processing of the digital stream...based on what people say. The M-audio doesn't. It passes the raw signal to the Surround receiver.
http://www.spacelofts.com/h30/mini-IMG_1968.htm
http://www.spacelofts.com/h30/index.htm
When you have it all setup do buy Terminator 2: Extreme Edition. It has a HD version that plays on WM9. It looks fantastic.
If you want to fully tweak you HTPC picture most people will use Theatertek with FDDShow or WinDVD with all the Dscaler and FDDshow tweaks. For an easy software DVD player that is almost as good as the above but is just a one step install use NVidea NVDVD 2.55 player. (Thats what I use)Make sure to also get Powerstrip to change your desktop to 16:9 to fit your HD television. Do see my HT links and you will see all output is via the HTPC.
I believe the only way to get HD on the HTPC is through a HD capable PVR/HD card or if you have a PVR card that accepts input from the HD signal from a STB.
http://www.keohi.com/keohihdtv/htpc/myhd/myhd_performance.html
