Can you please explain what you are trying to do / why you need to do it, and maybe we can help a bit. I know of no standard tools to do what you want as inter-domain logins are normally handled by trusts.
Ok, we have a ActiveDirecory called example.com our customer has a AD called testing.com, in the testing.com domain there is a OU with users in it.
What we want is to synchronize the users (and passwords) of the user accounts to a specific OU in the example domain.
It is possible to create a VPN between the sites.
granted, its been a while since i have had the need for this type server, but when i did, i used MIIS to sync the GAL between 2 different sites to have one large city directory (i worked for local government at the time, probably a thread here about it circa 2006 or 2007). it also allowed for accounts created for new hires to come log into the desktops at our office without us having to create accounts…