Setting up POP3 and Exchange accounts in Outlook 2003

We are using SBS 2003 Premium with Exchange Server 2003
and all workstations are notebooks running Windows XP and
Outlook 2003. The email accounts on all notebooks are
setup as follows:

POP3/SMTP (default)
POP3/SMTP
POP3/SMTP
Exchange Server

This worked since we upgraded to SBS 2003. We have now
upgraded hardware (2 new notebooks) and set them up as
above. The problem is that everytime the notebooks are
shutdown, the default email account becomes Exchange
Server and we have to change the default to POP3 account.
This does not happen when the notebook user is logged off
and then logs in again.

Thanks in advance,

Tony