In order for Entourage to continue to look up people in the U-M Online Directory after July 7, 2009, the LDAP setting must be modified in your Entourage Exchange account. You can accomplish this in 3 quick steps.
Under the Entourage menu, select Account Settings.

In the Accounts window, double-click the name of your Exchange account.

In the Edit Account window:

select Advanced.
in the LDAP server field, replace the entry with
ldap.adsroot.itcs.umich.edu
Click OK