log REMOTE_ADDR

[rstan]

The owner of one of the site I work on wants to see if a certain person is logging into his site. The problem is this person is most likely using a proxy ip. Is it possible to log this persons real ip by using $REMOTE_ADDR = $_SERVER['REMOTE_ADDR']; or somthing simular?
and save it in a text file....

[ShrineDesigns]

try:<?php
$remote_host = gethostbyaddr($_SERVER['REMOTE_ADDR']);
?>