Modify submitted values from user form before processing

function custom_user($op, &$edit, &$account, $category=NULL)
{
 
	switch($op) {
		case 'validate':
			if(is_array($account)) // checking to make sure we're only doing this on register.
			{
				$edit['profile_name'] = $edit['name'];  // setting profile name as username (name)
				$edit['name'] = $edit['mail']; // setting username (name) as mail address
			}
		break;
	}
}