Originally posted by manofsteal:
Ironically, even with Rendezvous disabled in Directory Access, I'm still able to chat via Rendezvous in iChat...why/how?
Because the previous post was bad info

Turning it off in directory access will result in it not being used for some searching, but it doesn't turn Rendezvous completely off.
There's no good "clean" way to do it. You can kill the mDNSResponder process (from Terminal or from the Activity Monitor application, and that will do it for sure. But you'll likely have to reboot to get it back.
You can also always turn off Rendezvous support specific to iChat from within iChat
