This page gives you basic information on creating a podcast, including a sample feed.
It's written with audio podcasts in mind, but the principles are the same. The only real difference is that the 'type' attribute in the 'enclosure' tag is different for different video formats.
To see the required type, please go to this page:
and scroll down a little to the 'enclosure' section.
For Video Podcasts it is best to have the file with the following settings.
640 x 360 resolution. H.264 Codec and .m4v encoding.
If using compresor or Quicktime pro - use export to iPod setting.
The above format is the most compatible format. It will work with Apple TV, iPhones, iPads, iPod touch, iPod Video, Zune, most android and blackberry phones.
This allows you to have one format that works for most cases and it keeps the file size downn so it still streams ok over 3G.
More info on Video encoding is here: