Each user account needs to be set up individually with it's own accounts. You can set up the same account for every user if you want but it would be very difficult to keep track of the emails as you can only view the ones opened using that user account. It is designed that way to allow every user to have the privacy of their own email account.
You will have to log onto your freeserve account and search for advice from there. It is usually simple to do (or is with Tiscali) I'm sorry but I don't know how Freeserve do their multiple email addresses.
In Outlook Express click on File / New Identity add new identity. Create the other mailbox there. Then all you have to do is to click on File/Switch Identities to move between the other accont(s). Then they switch back to the Master account. It works!