Hi, I kind of have the same problem. And it's the first time I update MW. Before the upgrade I had version 1.13.2 (yeah, I know it's a very old version) and PHP 5.2.17. I updated PHP to 5.4 and installed the update of MW to 1.20.3 the latest verion available. The installation process went well. Wiki recognized PHP 5.4 in the check of requirements for this version. then came the window: you can use MediaWiki now. When I clicked on that button the error "MediaWiki 1.20 internal error - Media Wiki 1.20 requires at least PHP version 5.3.2, you are using PHP 5.2.17" came.
I also waited one night because of what you wrote before, but no changes so far.
Please Help :)