One, from what I can see, Yahoo! Messenger 6 is most likely using the Host Name registry value as a fallback to when ConnServer's value doesn’t link to a working server. You’ll have to either make both values link to the server of your choice, or delete the Host Name value entirely.
Two, Escargot’s Yahoo! Messenger frontend is still being worked on, and isn’t public in any form yet. So you’ll have to set up the server locally and make sure that the registry values reflect that.