In 10.6, Apple moved Directory Utility to the /System » Library » CoreServices folder; you can launch it directly from there, if you wish.However, the “official” way to get to Directory Utility now is through System Preferences » Accounts » Login Options. At the bottom of the panel you’ll see Network Account Server; click on the Edit button and there is a listing of directory services. The button in the bottom left-hand corner says Open Directory Utility; click on this to launch.