OS: Windows XP and Windows Vista 

This is one of the most common questions I get asked after setting up a new computer;

What happened to the email addresses that auto-complete when I start entering an email into Outlook? They used to come up.

There are Windows Vista instructions   and Windows XP instructions

Windows Vista instructions

For Windows Vista

On the original computer go to drive:\users\username\AppData\Local\Microsoft\Outlook or drive:\users\username\AppData\roaming\Microsoft\Outlook.

In the folder Outlook, you can find a file named username.nk2, you can
copy this file to the same location on the new computer.

This folder might be hidden. To make hidden folders are visible on Vista;

1. Click on the Start button at the bottom left of your screen.

2. Left-click on Computer in the menu that pops up.

3. Left-click on Tools on the menu.

4. Left-click on Folder options.

5. Left-click on the View tab.

6. Left-click on Show Hidden Files and Folders.
7. Left-click on OK to close the window.
   

Windows XP instructions

Well fortunately Microsoft have written instructions on how to do this at http://office.microsoft.com/en-us/outlook/HA011394511033.aspx

The Microsoft instruct