Well many programs, tv tuners and such are supported by windows already, your just asking yourself for trouble looking linux supported drivers, but it is an option and some you should be able to find hardware to support linux.
Also, Xp media centre edition and Vista Home Premium is great for HTPCs.
A 4200+ is recommend in the gigabyte motherboard for blu ray playing. Unless you do a whole lot of encoding and ripping , a Phenom x3 (When if comes out) or Phenom x4 is a ton better. You don't want to be doing too much ocing and most people want to keep their HTPC's as quiet as possible with low end CPU's that require less power (Athlon BE 2300 @ 45w) and quiet CPU coolers.
Runnin' Stock, Cool, Quiet and Fast
Thermaltake Big Typhoon w/ Scythe Kama PWN Fan
MSI P6N SLI Platinum
OCZ Vista Performance Platinum 4x2GB
2x Western Digital Caviar Blue 500GB RAID 0
HD Radeon 3450 *Temp* *8800GT SLI Coming*
Acer AL2216W 22" LCD Monitor + 17" Samsung Sync Master 750
Antec TruePower Trio 650 Watt
Power Up Standard
Windows 7 Home Premium (64-bit)