How create Cross Domain with Open Directory 4?

Hi, in my company we 've just bought some xserve to create a cross domain authentication… but there's not any helpful documentation about how it does: just a plenty of marketing news about OpenDirectory 4 Cross Domain Feature!! We asked to our Apple reps and no answer… No helps from google… Anyone here who has successfully created a Cross Real Authentication between Active Directory (2003 SP2) and Open Directory Master 10.5.2 ... Any experience, suggestions and tips would be appreciated? Cheers Rick