iTunes 4.9 includes support for video podcasts, simply by having the RSS feed point to a .mov rather than an .mp3.
For an example, subscribe to the "Tiki Bar TV" podcast in the store. The downloaded file will have the video camera icon next to it in the iTunes browser. It plays just like a music video in the iTMS.
Mac OS X Hints
http://hints.macworld.com/article.php?story=2005063012244838