Using OWA 2003 w/SP2 on an Exchange 2003 w/SP2 server.

We seem to be having an issue in using OWA for users to access their
accounts from workstations that have Generic or Autologon logons enabled.  
The credentials remain valid even after the password expiration date, and,
users can still connect to OWA.

Our default Domain GPO has a password expiration of 90 days, so we assumed
tha t the logon to OWA wouldn't work after that time, but...it does.  Also,
we noticed that users logging on to OWA (the Generic or Autologon Domain
account gets them to the Desktop, then, multiple users will use OWA under
their own accounts to access their email) don't change the "Last Logon Date"
in ADS--like...they aren't authenticating, or something.

Is there something wrong, or, does OWA authentication not use Kerebos or
something?

Thanks!