Virtual directories or Redirect with POST

Howdy folks, after studing this mail list in an archiv for several hours and not found any solution, I will ask you directly. We want to handle sessions with virtual directories like: www.fubar.com/1iuz28si2/path/file.php. The middle of the path should be a dynamic generated session handler and rest of it is not in a public readable directory. So far so good.... After the php script (ErrorDocument 404 error404.php) is started, there are no parameter fields like $HTTP_GET_VARS and $HTTP_POST_VARS. Ok, you can create your own array by using the $REQUEST_URI, but where are the parameters after a <form method="post"> was used? Any ideas are welcome :) best regards Thomas