Um... aren't you missing a Tuner (HD) card? How are you going to recieve/record TV without one?
Get yourself a 10,000 RPM hard drive to boot / and run the OS from.
A Western Digital Raptor can be had on newegg.com for less than $150. When it comes to IO performance and getting your "Appliance" to boot quickly, this simply cannot be beat for what you get.
If you're interested in getting the cost reduced. I'd be happy to relay-ship you the parts. Customs can be handled as a "gift". Shh....
Yeah, I'm pretty much a speaker snob myself. The only "computer" speakers I've heard lately that sounded any good were Klipsch. My best advice is, buy what sounds good to YOU. Personally, the differences between a US $2000 speaker setup and US $500 setup are worth the money for ME. For others that I know, they can hear the difference (possibly because their ears are older / they aren't musicians). So, buying "better" is a waste of money.
I used to work selling consumer electronics. Many people would get lost in the numbers, and that made it easier to sell the more expensive stuff. But, honestly, given a blind test they wouldn't hear the difference.
Buy what sounds good.
Following up on Bob Archer's comment about a capture card. I just built an HTPC using the Hauppauge (sp?) PVR150 MCE capture card. It works pretty good, has hardware compression, and is pretty cheap ($110 Canadian). I'm not sure if the quality of the encoded video is quite what I want but I haven't had time to play with all of the settings to see if there's something I can change to fix that.
Overall, I'm happy with the card. The nice thing is that you can put multiple PVR150's in the same PC so you can watch and record at the same time (I think one guy did 7, yes SEVEN, cards in one PC and had it all recording at once).
I run GB-PVR, by the way. Great little app as I don't have a Windows Media Center license.
Why not C2D processor (if not E6300 then surely E4300). I bought E6300 and paired it with 800Mhz RAM and ABIT Pro MB. Gigabyte is also excellent choice. But C2D architecture is much more advanced than P4D
About speakers, although its a more expensive solution, I can warmly recommend Cantons line of compact 5.1 systems. You'll need to add an amplifier to your setup, but it'll be worth it.