I have used the following successfully with good results, and this setup is so quiet that if you are more than 3 feet away you dont know it is on:
Antec Sonata PC case (almost silent w incl powersupply) - $129
ASUS P4PE Motherboard (no fan on chipset) - $160
2.4ghz P4 w/512 memory stock CPU fan
Fan Controller (to reduce CPU fan speed) - $20
Seagate Barracuda 120gb - $60
ATI 7200 - $80 (requires no fan)
RME Digi96/8 - $250
The O/S is tuned for music based upon tips at
http://www.musicxp.net/. The 2.4ghz CPU is rarely above 10% usage, and so it runs cool and quiet at 104F with the CPU fan speed reduced (using the fan controller).
The RME digital card feeds an external DAC for my hifi using coax out, and a HT receiver using the optical output. Media Center ASIO mode is used with a 1.5 sec buffer size.
The ATI card feeds my HT projector. A very flexible piece of software to tweak video is Powerstrip. It allows you to tune the video output to the specific resolution and timing of your display.
My music is stored on a file server optimized for cooling (many fans), which is located in another room.
I don't use this setup for TV, but adding a fanless TV card, perhaps the one from ATI, should not be a problem.
Lynn