Interesting release on CodePlex earlier this month: the Podcasting Kit for Sharepoint. This kit allows you to more easily integrate a podcasting solution into SharePoint 2007.

Current release is still pre-beta but they are planning to have a production ready release by Septebmer 2008.
 
Some of the features are:

• Listen and watch audio/video podcasts, anywhere on your PC or mobile device (Zune, SmartPhone, or any podcasting device)
• Share content by producing your own audio/video podcasts and publish them on PKS on your own.
• Tag cloud
• Comments
• Rating system
• Play podcasts in real-time using Microsoft® Silverligh and progressive playback
• And more…

Definitely worth checking out before you think about creating your own solution from the ground up.

As the PKS uses WMV as a video format, you might also be interested in a side project, “Server Side Re-encoding for Podcasting Kit for SharePoint”, an add-on that converts several video and audio formats to WMV.