Sessions in URL not being recognized!

I have an existing production machine running Red Hat Linux 7.1, Apache 1.3.19, and PHP 4.0.6. I have a new machine I'm *TRYING* to replace it with. It's a clean machine that I just did a fresh install of RedHat Linux 7.1 on. I downloaded MySQL 3.23.47, PHP 4.0.6, and Apache 1.3.22. Everything seems to build and work fine. But when I copy all the php site files over to the new location, the sessions don't seem to work! I am not using cookies, and so the PHPSESSION ID is in the URL. The odd thing is, the sessions are created fine. I see the session file in the /tmp dir. I've inspected it and it seems fine. Same size and contents of the production machine. But when I go to a new page on the new box, the URL contains the Session id, but the code doesn't recognize that there are any session variables! It says my session variables are not there (session_is_registered fails!). I don't understand what's going on. I have rebuilt and reinstalled till I am blue in the face. I am literally at my wits end. Why is it that the PHP code isn't recognizing Session variables on the new machine?????? Track_vars is on. Register_globals is on. Any help would be appreciated... test code to run, whatever... Please help! -- Grant