Dual Profile Outlook setup keeps prompting for username+password

Administering a 10-user LAN running off a SBS2008 server using Exchange.
Very simple setup: Each user has an email address myname@domain.com with his/her Exchange email account set up on their pc using Outlook 2003.
A complication arose when I was asked to set up a new general email address enquiries@mydomain.com and give all users access to this. As everyone knows, you can only set up one Exchange email address per pc/profile. One option I considered was to set up a forward from enquiries to each user’s email; but what they wanted which that couldn’t deliver was for each user to be able to see whether someone else had replied to an email to enquiries@ to save multiple responses.
What I ended up doing was setting enquiries@ as a new Email Profile on each pc. On launching Outlook, they are given the choice of which profile to use, either their own or Enquiries. This works well with all users happy: When launching the Enquiries profile, each email in Inbox shows if it has been replied to or not.
There is one annoyance and it IS annoying, which is that, every time they launch Outlook now, if the profile they choose is not the one they chose last time around, they’re presented with a logon username & password box, which they have to enter every time. On the Windows 7 pcs, this is pre-populated with the username corresponding to the profile they chose last time they launched Outlook; On the Windows XP pcs, the username box is blank, which is marginally less annoying as at least they don’t have to delete it to get the correct username keyed in. But it is an annoyance they could do without. I’d hate to have to tear up this chosen method of getting the enquiries to work, as it took a lot of doing to come up with a solution which suited all 10 users, believe me! If only there were a way / registry hack / whatever, that could make it dispense with the need to prompt for the username & password every time!