How does the Windows Address Book work cross-forest?
By default the “Active Directory” ‘account’ within the “Find People” applet searches the workstation’s forest. This can be configured to search any arbitrary LDAP provider, including the user’s forest, by modifying the properties of the “Active Directory” ‘account’, or by creating a new ‘account’ to search the desired directory. These providers or accounts appear to be stored in HKEY_CURRENT_USER\Software\Microsoft\Internet Account Manager\Accounts so if you wanted to automate this configuring this, you could use a logon script to do it.
