HTPC advice

I have an old PC that I was hoping to use as a HTPC because it is the only PC on my network that has a DVI output. I have a 720p DLP projector and I would like the best connection (digital) for DVD playback and for PC Games. I need help spec'ing a system that will work for my needs as follows:
1.) DVD playback via DVI/HDMI output to projector. Would like to be able to use ffdshow w/ theatertek to get the best PQ (thats why I cant use the old PC, its a P3 996Mhz)
2) Graphics intensive PC games like BF2, HL2 etc
3) connect to external network drive to play stored DVD's (Firewire or 10/100/1000 Ethernet?)
I dont need a TV tuner because I will be using an Xbox 360 as a MCE 2005 Extender for that. I have two networked PC's running MCE 2005 although neither has a DVI output that I can use on the PJ.

Also, does anyone know of any guides out there for building such a system? The only ones I have found so far are for building a MCE system which I dont really need and for systems that arent very good for graphics intensive PC games.

Thanks for any suggestions.