Brian Tirch is any army contractor work very closely with the Beta team here at Microsoft. He wrote a great article on how to have the Outlook client use a static autodiscover.xml file. If you have time check out his blog here: http://exchange-genie.blogspot.com/2007/07/autodiscover-ad-attribute.html
Dave
An easy way to remove (some) entries from the autocompletion list in OWA 2007 Exchange Server Public