Managing Mulitple User Accounts in Outlook Express - can this be true?

I bought a friend a PC off eBay to save them money and set it up with XP Home.  I thought that was the end of the deal but apparently, in their opinion, I'm also obliged to provide unlimited training and technical support!

As requested I created three user accounts in XP all with email (Outlook Express) set up, all using the same email account, all fully checked and working.  A week or so later I got a call saying that email wasn't working for two of the users.  

I opened Outlook Express and was immediately presented with a new window with a drop down list of the three Users and I had to choose one and enter a password and at that point Outlook Express opened, its kind of an account management thing, completely redundant in XP but something that got installed because "that's how it was on our old PC so I just did it".  The User has not created any new email accounts and there was only one account on the old PC but alleges that by using this account management thing the other two Users have now got individual email with their own addresses - how can they have?

I really don't see how this thing can work and am not surprised that the other two users now have screwed up email.  The friend who set it up is not stupid but is absolutely useless at explaining problems and when I asked how it has been set claimed they have "forgotten".

I have spent what seems like hours trawling the internet for advice on where this account management thing comes from but all my searches end up with advice on how to check multiple email accounts which is not related to this problem.

Any advice on what this thing is and how it should be set up properly would be gratefully received.