Jennifer,
Russ is "spot on" with his response to you. If you want to find it so that
you can do the renaming suggested, follow these instructions.
Your autocomplete file bears the same name as your MS Outlook profile name
and has an extension of nk2. Further, it is found in your Documents and
Setting Folder.
(Make certain that in your Folder settings, you can view hidden and system
folders.)
Here's where you can look for it manually:
Docs and Settings\Your login user name\applications\Microsoft\Outlook.
When you go to that directory, there should now be at least one file with an
extension of NK2.
If you wish to search for this file, start your search dialogue, and select
Advanced Search options to search for Hidden and System files. Next, you
should look in your Documents and Settings folder and search for *.nk2.
Another clever way to find that files is by typing:
%userprofile%\application data\Microsoft\Outlook in your Windows Explorer
address line.
Hope this helps!