[MarkG]

i've moved to a new server and this code doesnt work anymore for some reason

if it you can get it working either here's another way:

1) set a 404.php as your 404 handler in your .htacess or httpd.conf

ErrorDocument 404 /404.php

and put this in

<?
ob_start();
if ($ref=="") $ref=$REQUEST_URI;
if (preg_match ("#/forums/t\d*-s.html#",$ref)) {
        $ref=str_replace("/forums/t","",$ref);
        $ref=str_replace("-s.html","",$ref);
        Header("Location: http://domain.com/forums/showthread.php?threadid=".$ref );
}
if (preg_match ("#/forums/f\d*-s.html#",$ref)) {
        $ref=str_replace("/forums/f","",$ref); 
        $ref=str_replace("-s.html","",$ref);
        Header("Location: http://domain.com/forums/forumdisplay.php?forumid=".$ref );      
}
ob_end_clean();
?>

important: my forums are under /forums and i have my links like t4444-s.html not t4444/s555555.html (with a - not / and without the session number). change the code according to your situation

if anyone uses it, let me know if it works for you

ps. there one issue with this sollution: you still get a line in your error log about a missing file...