The vhosts will need to be updated to serve to the new url, unless he just uses a CNAME doing it that way.It's rather simple, just point the new domain to your current hosting account and change the board details in the ACP.
Your host should be able to help with pointing the new domain to your current account.
Thanks Jake, all seemed to be going well until I received an error when trying to email my users via AdminCP:Correct. No db stuff if it's the same server / hosting account.
Server Error fwrite() [function.fwrite]: send of 6 bytes failed with errno=32 Broken pipe XenForo_Application::handlePhpError() fwrite() in Zend/Mail/Protocol/Abstract.php at line 324 Zend_Mail_Protocol_Abstract->_send() in Zend/Mail/Protocol/Smtp.php at line 385 Zend_Mail_Protocol_Smtp->quit() in Zend/Mail/Transport/Smtp.php at line 144 Zend_Mail_Transport_Smtp->__destruct() in XenForo/FrontController.php at line 310 XenForo_ControllerAdmin_User->actionEmailSend() in XenForo/FrontController.php at line 310 XenForo_FrontController->dispatch() in XenForo/FrontController.php at line 132 XenForo_FrontController->run() in /home/hackslas/public_html/admin.php at line 13