Keith blogged about the Web Service Security Guide earlier.  Don Smith just blogged about a series of webcasts based on this guide.  The first one titled Securing Web Services with X.509 Certificates in WSE 3.0 was recorded and you can find it here.  There are two more coming up titled Securing Web Services with Kerberos in WSE 3.0 and Authentication to Web services with UsernameToken in WSE 3.0.  You can get all the details here.

-Marc