Robbie--
Looking at the policy template files in the Office 2003 Resource Kit (http://office.microsoft.com/en-us/assistance/HA011513601033.aspx), I do not see
anything that allows for permissions or delegates to be specified.
I also looked into the capabilities of the Outlook Security Features (http://office.microsoft.com/en-us/assistance/HA011402911033.aspx) that ships with
the Office 2003 Resource Kit and I didn't see anything there as well.
If all you wanted to do was modify folder permissions and not do anything with delegates, then you might be able to use the PFDAVAdmin tool (http://www.microsoft.com/downloads/details.aspx?FamilyId=635BE792-D8AD-49E3-ADA4-E2422C0AB424&displaylang=en)
to set the appropriate permissions across multiple mailboxes. Of course this is not automatically done like GPO is, but it might work for what is needed.
I did try looking through some of the Outlook Newsgroups about this, but did not find anything more. I don't know of any Outlook specific Blogs, so I did not check there.
--Chris