You are using two very different versions of Outlook.
At work you are using Corp/Workgroup mode, which uses the Outlook Address
Book.
At home you are using a simpler version, Internet Mail Only, which is unable
to support the Outlook Address Book and must use the Windows Address Book
instead. You can switch to the full version if you want.
For information on choosing a mail support mode or changing to the other
mail support mode, look here:
http://www.slipstick.com/outlook/choosingmode.htm