Most results I get on google is how to get both versions running simultaneously on the same server but at different URLS but that's not what I want.
I'd like, for example, to get
http://localhost to run PHP4 and PHP5 at the same time on the same site. This is because I have a website that has old code from PHP4 that breaks up when executed in PHP5.
The same site also has some components written only in PHP5, so I would like to run both PHP versions at the same time in the same site.
I'm on Windows XP running Apache, I wouldn't mind switching to IIS7 if it's required.
I'm already aware of the security risks associated with this potential solution.