I want to build an HTPC for playing back xvid/divx video files, music, and maybe surfing teh internet and checking email. I have a Pentium D 820 processor just laying around. I dont need tv viewing, recording, or to be able to play games on it. Just need it to watch movies and play music. Any suggestions or help is appreciated.

If you're planning to run Vista then the 8400/8500/8600 Nvidia cards are your best bet. With the right decoder your old pentium will likely do just fine. They are the most future proof for decoding the newer codecs.

The hardest think I had with my HTPC was finding a case I liked.

If DivX and XviD is all your going to play then any video card will do even onboard video. If you plan on watching Blu-Ray or HD-DVD then forget it. You'll need a C2D E6600 or Athlon 64 6000+ if you want to avoid dropped frames.

The case and mobo depends on the size, full ATX or micro-ATX.

You'll probably want a quiet PSU. I recommend Seasonic S12 PSUs. They are very quiet and reliable but more expensive than the average PSU because they are premium quality PSUs.

I prefer a discreet sound card rather than on-board sound so go for a Audigy 2 or X-Fi.

Go at least 1 gig ram. Around 50.

For anything HD, then any Nvidia graphics card in the 8xxx or any ATI card in the 2xxx. That can be anywhere from 150 to 500 or so. If no HD, then i would say anything around the 100 range would suffice. Anything more would be overkill for this. Don't forget the highest quality video connection cable (DVI or HDMI).

The most hard drive space you can put your money on. Not only to store you media but, more importantly, backup your media. You might want to go raid 0 with at least 300 gigs (or whatever is your sweet spot in disk space) and backup to another drive(s). You can get 250 gig drives around 60 bucks each. You can also get a 500 gig drive for 100.

With the large amounts of data you will be tossing around, you may want to go with Gig ethernet ports and upgrade your existing network to that as well. If your using wireless to this machine, then invest in a high quality wireless router. Most current MB come with Gig ethernet ports.

I'm not too familiar with what is the quietest PSUs, video cards, hard drives, and etc as far noise levels go but silence is golden for this thing. Make sure you do some homework on this. Last thing you want is to shell several hundred dollars on a Home Theater PC and you end up hearing your PC over your favorite song or movie.

As far as a case and a psu goes, I would suggest anything shuttle makes. If you haven't heard or seen a shuttle, you will be amazed on how they shoved everything in a shoe box. you can get a barebone system from shuttle (comes with an above-average MB and PSU) between 250 to 500.

You will also need a decent to above average sound card. shuttle mb's come with above average onboard sound. But any creative sound blaster x-fi would do wonders. Maybe some above average speakers and/or headphones as well. If you can afford it, go with some bluetooth headphones.

Wireless keyboard and mice. Go bluetooth if you can afford it.

I think that will do it. Again, shuttle's makes barebones that lay an excellent groundwork for this line of PCs. Many of them actually do fit in an entertainment centers.