You would create a PHP file (.php) in your directory somewhere, then past his code in there, and save it. So, when you view your saved page, it will show your IP address. :P
Actually, this won\'t grab the real ip (on all ocassions). Not all proxies store the real ip of the user in HTTP_X_FORWARDED_FOR. However, this is much better than going by just HTTP_REFERER. Not bad ;)