I've got Desktop 4 w/SP1. When Desktop manager starts, it hangs on Connecting to Messaging System. I've tried the clean uninstall (registry, folder, and all) and have removed my Outlook profile and completely rebuilt it, too. The current install of DM on my machine is fresh as of about an hour ago. I'm running win xp pro sp2 with all the post sp2 patches and Outlook 2003 in cached exchange mode against an exchange 2003 server.

I did connect a few other BBs to my desktop a few days back in order to delete everything off them, but I never told DM to switch anything to those PINs.

Anyone have any ideas?

Try creating a new MAPI profile that is not using Cached Exchange mode, at least for initial setup.
Be aware, If you use DM to create an encryption key while in cached exchange mode, the new key is written to the local machine instead of the User Mailbox on the Exchange server which can cause sending issues.

BTW: to delete everything without connecting to desktop - perform a handheld wipe direct from the handset.
Either with "wipe handheld" [options=>Security=>(wheel)]
or enter a password incorrectly 10 times (just add a password if passwords not in use).
All user data will be erased but the OS + applications will remain untouched