All url-syntax variants :
redirect.php?address=../index.php
redirect.php?address=/forum/index.php
redirect.php?address=http://www.pr.c-php.com/forum/index.php
redirect.php
<?
# File : redirect.php
$address=$HTTP_GET_VARS["address"];
if ($address == "")
{header("Location: http:/forum/examples/straight.html");
exit;} 
else
{header("Location: $address");exit;}
?>