Change default mailbox in Outlook/exchange

Reading your description, I assume user B is using the same user account as user A?  I assume you don't want user B accessing user A's old emails?  If so, then the best way would be to create a new user account.

If all you are wanting to do is create a new default email account on the same user, open up Active Directory, goto user properties on the selected user.  email accounts tab, create new email address and select the default button.

Outlook will load the user details for the account that is logged into the PC.

Can not create new user account, does not matter if user B access user A's email. This is a Windows NT domain so no AD. All I need is when I open outlook user B's mailbox is the default. The account that this machine uses is an Admin account I am setting up an old Version of ACT! and I need the syncmaster email to be the default on this machine.

I'm gussing you are running exchange 5.5??

Yes,

I'm not sure where the client is keeping the users info. I just want to wipe this system clean of this account reinstall outlook and setup user B? I thought by uninstalling outlook all the old setting would be gone and I could just setup the new account?

Thanks