Enable Vista's hidden administrator, and password-protect its XP equivalent is the blog for just that seen at
http://www.cnet.com/8301-13880_1-9870793-68.html
The alternative besides following the advice in an article like this would be to buy a retail software for the same purpose like the one seen at
http://www.folder-password-expert.com/
That's even quite a bit cheaper then the $149 license fee for the one seen at
http://anticrack-software-protector-....qarchive.org/
In Vista that's referred to as Windows Mail there no longer Outlook or Outlook Express.