I have posted before about nailing together a dedicated media center computer using XBMCBuntu - a slimmed-down Ubuntu Linux installation with XMBC ready to go. Basically, grab an old PC and a suitable (cheap) video card, and load up XBMCBuntu. It's great fun and I have really enjoyed playing with it. Today, I saw not one but TWO posts concerning XBMC, and both were actually quite interesting - I already installed the Hulu plugin from the second article. Excellent!
LifeHacker - make XBMC easier to use for non-geeks
HowToGeek - how to get Hulu and Amazon video on XBMC