Hmmm.... CMIIW, but I think You can install more than one version of PHP in one computer, although You can only run one at a time.
Simply edit Apache's httpd.conf file. If I install php 4.3.2 in C:\php432, then i'll write :
ScriptAlias /php/ "c:/php432/"
or
LoadModule php4_module c:/php432/sapi/php4apache.dll
If I install php 5.0.1 in C:\php501, then I'll change the directory to c:\php501.
And of course I have to overwrite the php.ini file in the Windows directory with the one I use.
Note :
- I havent install php 5 though :p So maybe the config is a bit different...
- I always failed running php as an Apache module... :p