Perhaps I'm missing something obvious here, but you authenticate basically to a "domain". All of the domain controllers in the same domain have the same information. You can set up a "preferred" controller, but the results should largely be the same, modulo some 2008 functionality. The connection to the current domain controller won't be broken without a reason. The CLI gives you the option to reset this connection. Give the manpages a read. Even with all of this, it is still just a "preferred DC" so there is no absolute deterministic behaviour there. If you don't want to use the 2003 controller, turn it off.