Architect Webcast: Securing Web Services (interwise recording)
Support WebCast: Introduction to Microsoft Web Services Enhancements (Windows streaming media)
This one is good if you've been into soap headers and such before:
Support WebCast: Microsoft ASP.NET: Advanced XML Web Services Using ASP.NET (Windows streaming media)
And this is an older, but very good article that describes the different proposed security specs around web services.
If you know of good webcasts about WS-Security, please comment.