I'm more concerned about Outlook 2003 than Outlook Express. I need to change the "leave a copy of messages on the server" setting and I don't want to go manually to each computer and do it.

I imagine it's somewhere in the registry in a path like this:
HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\Windows Messaging Subsystem\Profiles\Outlook\

Unfortunately, that path is filled with stuff like this:
9375CFF0413111d3B88A00104B2A6676\00000007
which, I'm guessing, differs from one computer to the next.

I imagine it could be done with a GPO, but we're running Linux and Samba here, and I think the best I can do is a logon script. The script can, of course, run whatever programs I want. Is there a way to do it from the command line, or a program that can do it that can be started from the commandline (even if it runs in GUI, as long as the user doesn't have to do anything)?