We're having trouble getting a new Windows 7 Ultimate machine joined to an OS X domain.
I found this Apple KB article discussing the very same issue we're having.
Basically, when entering all the information to join the domain (which all works fine on XP and Vista) we're receiving a "domain does not exist or could not be contacted" error message.
I also changed two local security policy settings per this article that are known issues between Windows and SMB authentication.
Has anyone else successfully put a Windows 7 machine on an OpenDirectory domain?