http://insideoe.tomsterdam.com/files/wab.htm#share
Sharing the Contacts folder in Outlook
If there is no path shown in the Address Book under Help | About Address Book, that means you have set OE to share the Contacts folder in Outlook98 or Outlook2000 and so no *.wab file is used. Sharing allows OE to display only the Contacts folder in the default *.pst in Outlook's default Profile. You can't access other Outlook folders, just the Contacts folder, and there is no support for using Shared Contacts amongst multiple OE Identities. To turn off sharing and revert to using a *.wab, click Tools | Options (which appears only in OE5/5.5 and only if Outlook98/2000 is installed and configured in Internet Mail Only mode). However, starting with OE6 and Outlook 2002 (OutlookXP) and Outlook 2003, sharing is no longer officially supported. If you install as an upgrade and sharing is already enabled, it will remain enabled after the upgrade (or at least, it should). Therefore the Tools | Options has been removed from OE6. In that case, you can still manually enable (or disable) sharing by editing this registry key after closing Outlook Express:
\HKEY_CURRENT_USER
\Software
\Microsoft
\WAB
\WAB4
Create a new DWORD value named UseOutlook, or modify that value if it already exists. To enable sharing, so that OE no longer uses a *.wab, set UseOutlook to 1. To disable sharing, set its value to 0. The change will be reflected the next time you open OE.