So this would primarily be a PC for downloading torrents, watching dvds (have a drive) and surfing the web. No serious gaming, most likely no overclocking. Also dont have cable TV (and dont want it) and get no reception so dont need a tuner.
Will all this stuff fit in this little box? Will it stay cool enough to use? Will it be quiet? What are better component ideas?
It all looks good to me. Maybe a bigger hard drive if you plan to rip DVD's or Blu-Rays.
A couple things missing from your list. I don't know if you already have them:
Wireless keyboard/mouse (I recommend getting one with a built in trackball or touchpad) such as
Adesso WKB-3000UB (w/scrollwheel for web page scrolling) $60
or Moneual MK700 (no scrollwheel) $30
Also, a remote control is a must for any HTPC like the Microsoft MCE remote $30-40
And finally, you didn't list a front end/operating system. I suggest you go with Vista premium. The media center in Vista is pretty darn good. If budget is a concern, then there are linux distros with MythTV bundled if you are linux savy.
Additionally, I would recommend keeping all your media file physically separated from the OS; meaning seperate hard drives. That way if on drive fails either you'll lose your OS or your data, but not both.
Also, since you will be doing a lot of downloading, recommend saving the data to the OS drive. Once the download is complete have your torrent program move the downloads to your data drive.
My HTPC has 4 hard drives. One for the OS, two for Data, and the 4th drive is my "thrash" drive where all downloads are initially saved to, DVDs ripped to (to be encoded), and where the swap / page file is written to. Having the "Thrash" drive minimized wear and tear on the OS drive and especially the Data drives. The only time when the Data drives are accessed is when I save media that have been completed encoded, or when I am accessing my media files. In this case I expect my "thrash" drive to die first, thus minimizing potential data loss.