This applies to Outlook 2003
If you create a new Outlook Profile, you may notice that when you start typing in a name in the To field, you don't get the suggested names like you used to.

Here's how to get the suggested names (ie autocomplete) back.
Exit Outlook 2003
Go to c:\Documents and Settings\user name\Application Data\Microsoft\Outlook
If you cannot see this folder, it may be hidden. Here's how to view hidden files.
Click Start, and then click My Computer.
On the Tools menu, click Folder Options.
Click the View | Advanced settings
Under Hidden files and folders, select Show hidden files and folders.
Right-click profile name.nk2 for the new profile and rename it to profile name.old
Right-click profile name.nk2 for the old profile, and rename it to profile name for the new profile.
Example,
Old profile - Outlook.nk2. Rename this file to Outlook.old
New profile - OutlookNew.nk2. Rename this file to Outlook.nk2
The nk2 file contains all of the autocomplete information for Outlook. Renaming the files will associate your old autocomplete information with your new profile.
Once you have renamed the files, open Outlook and you should be able to see the autocomplete information you had in your old profile.