I have seen folks in the newsgroup seeking assistance in deploying Internet Explorer 6.0 using WSUS. As a matter of fact, WSUS only supports security updates aka patches and hotfixes to a particular application (categories) or Operating System and it does not support Application / OS upgrades.
Microsoft has another product called SMS to do such tasks.
UPDATED (April 26, 2006):
Bobbie has posted an update on microsoft.public.windows.server.update_services
Bobbie Harder (MSFT):
I should mention folks on the question of upgrading IE via WSUS – we do have future expectations of being able to support this in future versions of IE. No precise timelines known now but it is under heavy consideration and a key ask from many of our customers.
How to deploy Internet Explorer without local administrator logon
Internet Explorer Administration Kit Home Page http://www.microsoft.com/technet/prodtechnol/ie/ieak/default.mspx
HOW TO: Deploy and Manage Internet Explorer 6 Service Pack 1 on Windows 2000-Based Computers
What can you expect in WSUS 3.0?