First off, out of the box, you get to share your popcorn as a network share (Samba).
Second, you need to get the NMT (Network Media Installer) – intro here and actual site here. Using this, I installed the supported version of Transmission and TorrentWatch-X in a couple of minutes (note to self, TorrentWatch-X requires you to add individual shows as favorites in order to download them automatically, took me a while to figure out!).
Third, YAMJ is a great addition – see here http://www.networkedmediatank.com/showthread.php?tid=35678. Looking at skins took me a while, especially since I run an old SD TV, I have settled at least temporarily on a skin called sd