I figured out how to do this, thanks.
<?
if($_SERVER['SERVER_NAME'] == '127.0.0.1')
{
echo '<script>';
echo 'window.location="http://www.yahoo.com/"';
echo '</script>';
}
if($_SERVER['SERVER_NAME'] == 'localhost')
{
echo '<script>';
echo 'window.location="http://www.google.com/"';
echo '</script>';
}
?>