If you are using outlook express, you also need to backup the following registry keys for each user on the machine. If you only back up the files, you won't have access to your e-mails, without a lot of jumping through hoops.
HKEY_CURRENT_USER\Identities\
HKEY_CURRENT_USER\Software\Microsoft\Internet Account Manager
HKEY_CURRENT_USER\Software\Microsoft\Outlook Express
HKEY_CURRENT_USER\Software\Microsoft\WAB\WAB4\Wab File Name
When you restore the mailbox data, it must be restored to the exact same file system path. Oh, and the regsitry data must be restored before you first run OE - otherwise you will have to delete all of its new blank registry entries.
Don't forget to backup the address book - seach for *.wab