Outlook 2003 on RIS imaged PC

I have created a RIS image for deployment to a bunch of new PCs we received
recently. I thought I had this particular image looking pretty good, but
after having the image deployed in the general user population for a few
weeks I have found a problem with Outlook 2003. Existing users of our network
are not affected by this problem, as they already have a user profile. This
only affects brand-new network users whose first network logon is on one of
these particular ris-ed PCs (so obviously the problem is with the default
User profile on the RIS image). Anyway, the problem is that when they open
Outlook for the first time, rather than being taken to their own mailbox (we
are in Exchange 2003 environment), Outlook tries to open the administrator
mailbox (I did all the pre-riprep profile configuring while logged on as
administrator). I know I could fix this by deploying the image to a new PC,
fixing it up and the riprepping again, but I don't really want to do it this
way if I can avoid it (....long story, but basically the rest of this image
works really well, and I'm concerned that I'll break something else if I have
to go through the process again....also, my boss wants the new batch of PCs
we just received imaged and deployed NOW.....not in a couple of days).

So.....is there a registry tweak or something I can do to the registry hives
of the riprep image to make it look for the %username% mailbox rather than
the administrator's on first Outlook run?