In addition to the problems discussed so far that relate to migrating OO code to PHP 5, some other changes break backward compatibility. Most of them are harmless, but it's better to be aware of them.
The name of the CGI binary file for Windows has changed. This change has no effect on scripts, but rather on the setup of a Windows server running the CGI version of PHP. The CGI executable is now called php-cgi.exe rather than php.exe.
In addition, the location of the CLI executable changed. It was previously located in the CLI subdirectory in the distribution (cli/php.exe), but it's now located in the main directory, the same directory with php-cgi.exe.
Besides this name change, ...