Outlook 2003 hangs on exit

I recently insallted Office 2003 (including Outlook 2003) on a brand new IBM desktop machine running Windows XP Professional.  Everything works fine except that Outlook 2003 "hangs" on exit.  The icon stays in the System Tray, and no error message is issued.  When performing an "Alt-Ctl-Delete" Outlook doesn't list in running Applications, but is in Processes.  To force an exit of Outlook I must terminate it from the Processes tab, then reload manually.  (BTW, I also purchased two new identical IBM ThinkPad Notebooks and installed Office 2003 over Windows XP Professional on each.  One of them has this exact same problem, the other doesn't.)

I've done a fair amount of research on this issue and can offer the following information I hope will provide some insight:

1.  No MAPI software is running to my knowledge.
2.  I've tried repairing the Office and Outlook products.
3.  SP2 is in place and running, as are all other operation system software and Office updates.
4.  I connect to an off-site Exchange Server using RPC over HTTP.  (I have tried connecting through a VPN and not using RPC, but I have the same problem)
5.  I'm using a high-speed DSL service and have 6 machines connected on a home network.  Three of the machines have the problem, three don't.  (Two of the machines having the problem and one not having it are located physically in the same room.)
6.  I've also tried running Outlook with the /noextensions option, but with the same result in hanging on exit.
7.  I've also tried unchecking "Send/Receive on Exit" to see if this makes a differance, but it doesn't.
8.  FYI, I am using the cached Exchange mode and an .OST for use offline.  I have changed those settings as well and no change.

I would really appreciate any help you can provide.  I have found a shareware product, KnockOut, that does help me monitor whether Outlook and/or Word are still loaded, and will help me terminate either or both to expedite a reload, but I don't want to have to rely in this additional step forever.