Almost, but not quite.
You should not lose anything. All your Outlook data (calendar,
contacts., mail, etc.) is kept in a single file called a "Personal
Folders" file, whose extension is ".pst". In Outlook, click
Tools>Account Settings and selectthe Data Files tab. That will tell you
where the PST resides. The Windows folder you see there, if you
accepted defaults when you first installed Outlook, is a hidden folder.
To see its contents, either enable viewing hidden files and folders (in
Control Panel) or open WIndows Explorer, in the Address field, enter
%LocalAppData%\Microsoft\Outlook
and press Enter. That will display the contents of the folder whether
or not you've enabled hidden files and folders. With Outlook closed,
make a copy of that file to, say, Documents in case anything goes
wrong. Then, in Control Panel. use the Mail applet to create a new
profile. This should help:
http://www.outlook-tips.net/howto/profile.htm . It speaks of Outlook
2002/2003, but the process is quite similar for Outlook 2007. After
creating the profile, the Data Files tab allows you to include your
existing PST in the profile (so you have all your stuff) and the E-mail
Accounts tab will allow you to redefine your account(s). One side
effect is that if you had the account in your previous profile
configured to leave messages on the server, your new profile will
download them all again. If you had the option set before, you'll want
it set again, of course.
Here's a site you may find useful:
http://www.outlook-tips.net/beginner/index.htm