Problems upgrading PHP..

So I'm trying to upgrade PHP from 4.0.1 to 4.2.0 on a box I have that had Apache 1.3.12 preinstalled, the source isn't on the box. mod_so is installed, so I just grabbed the new PHP tarball, unzipped it in /usr/local, and started compiling with the options I want, successfully built it, overwrote the old libphp4.so with the new one created, copied over the php.ini file with the new one, and restarted. It loads up fine, but sessions don't seem to work -at all-. Even variables I tack onto the end of URLs seem to get lost, which renders just about everything I've done in PHP inoperable, it just seems to lose these variables or not keep track of them to begin with. What did I do wrong? Chad