I don't know about email but with NT when you go into the user manager they have an option for you to "rename" the account. Highlight the account, don't open it... then go to the menu bar "User>rename" this should allow you to rename the user account and let the user retainall of his settings.
With email, you need to contact your exchange administrator and have her create an account I believe....
hope this helps!
Tdiva