outlook has a feature that help you fill in email address as you type.
The email addresses come from a type-ahead list that is populated as you send emails to people.
Windows XP, Server 2003 & 2008 the file can be found in:
C:\Documents and Settings\USERNAME\Application Data\Microsoft\Outlook
Windows Vista, Windows 7, Windows Server 2008 R2 the file can be found in:
Simply locate all of the files with the extension “NK2″ and copy them to your new computer or back them up before you reload.