If you're trying to search to see which object in AD holds a particular property, then Exchange guru Jim McBee's post on solving the "email address already exists in this organization" error should be a big help.
Using the custom search functionality, you can search for any arbitrary property or build your own complex query. Jim shows you how to find SMTP addresses added by Exchange, but you can adapt it to just about anything, as long as you know the right properties to search for.