I can confirm that the:
BFG Tech 7600 GS 512MB AGP Card
Intel D850EMD2 motherboard w/ Audio subsystem for AC '97 processing using the Analog Devices AD1885 codec
Linksys LNE100TX 10/100 Ethernet PCI Card
Are all 100% LinuxMCE compatible!
Also, I would greatly recommend the Antec NSK2480 case as the setup was easy. The case is sleek and looks beautiful on my home theater stand. Make sure that your graphics card is not a power hog as this case only has a 380w PSU. However, the PSU can be swapped out with another ATX PSU.
What I need to know is 100% LinuxMCE compatible:
Sound Card w/ SPDIF coaxial and optical outputs (PCI Only)
Wireless Network Card <--- My core is in the living room and my router in the bedroom.
Remote Control (that is not $150, sorry Fiire)
An extremely Heat Sink and Fan that fits a Pentium 4 - 478 Socket Processor