I had occasion to set up a dev box to test a new web application against different php versions, so I thought I would share the steps. This setup is for one PHP version at a time, and I have documented for 2 versions, but more can be done if required. Also I have used PHP4 and 5, but it could be multiple versions of PHP5, such as a beta version of 5.3. This setup was done using Apache2 on Windows.
Read more 'Switching between PHP versions with Apache on Windows'.