I've been thinking of doing a media pc in the living room. Have a i5 2500k w a ATI 6950 that never gets used. What would be the best way to start with that?
Get the tiniest enclosure you can, there are a bunch on newegg. You can hook up a OTA antenna if you want to get the local channels in HD, and all the media software supports PVRing stuff too. Worth it for sports and stuff, other shows are all torrentable. Get a cheap bluray drive in it too ($40 or less) for those random DVDs or audio CDs. Get at least a 2-3TB drive, with room for a second drive in the future. Internal is better than external imo.
If there is any way to have a wired connection for your media PC, do that. Wifi is ok, but you will end up waiting for shit and wifes don't like that, plus remote desktop control is much faster over wired. Wifi will work fine though, just have to plan ahead a little more. As said get a nice wireless remote, you can use a ultraslim keyboard/mouse combo one but for the wife I'd suggest using an iOS or android app, if she has a smartphone. or a ultra simple bluetooth/IR logitech remote.
I'd recomend plex or windows media center as your htpc software. You will want to think carefully about how you "feed" video in, you want to do it as painlessly as possible. Suggest a large enough hard drive on the htpc itself (not your main PC), and a torrent software that supports remote access. Setup RSS feeds from your favorite torrent sites, and use the HTPC frontend, android access, or your main PC to pick and choose which torrents to download, and delete. You really want the torrents to be right on the HTPC itself, copying them back and forth from your main PC gets very tiresome. The HTPC can act as a share as well to feed ps3, roku, boxee, etc to other TVs in the house or to smartphones/tablets/laptops.
Obviously setup your firewall to allow your htpc torrent access, remote torrent sites will see both your main PC and htpc as the same "source" so you can download from both no problems, at least I have so far.