If he's still getting the error saying the site doesn't exist, it may be one of two things: 1. wait another day or two for the DNS records to finish replicating or 2. (if using a PC with Windows) start->run->cmd then type
ipconfig /flushdns
That will flush the local cache and force it to contact the provider's dns server to get the correct address.
If that doesn't work, it may be his provider still has the old record. Only time will fix that. Usually no more than a couple days.
For grins, he can also try accessing it by IP address (not sure if the forum software will allow that):
http://174.123.200.146 [Edit: The server must be set up with host headers, as the IP address just brings you to the default apache page, so that won't work]
Pete