AD user login hangs when bound to OD

All our users and their home folders are stored on an Active Directory server. We want to use our OD to manage the Macs. When I bind a Mac to the to AD, user logins work really quick. But as soon as I add the OD user logins just hangs with a blank screen. An ideas?? The Macs are running 10.5.5 as is the Server.