[Courtesy of my friend and colleague John Canning, who isn't blogging but should be -- especially about his world traveling photographic expeditions...]
Here is a resource we nailed for the 2004 version of Media Center and revised for the 2005 version. If you want a great primer on Media Center features, check out the Windows XP Media Center Edition 2005 Reviewers Guide (Adobe PDF). It's chock full of screenshots, illustrations and information. If you want to know all about Media Center before buying OR have already bought and want to know what you've got this is the resource to have.
Reminder: This blog will be moving soon to http://blog.retrosight.com.