This all boils down to URI/URLs.
Step 1.
Apache only handles calls when the URI starts http://<some reference to your computer/
Step 2.
Apache only runs the php scripts when the mime type is php (generally when the URI ends with .php or whatever else you have put in your httpd.conf file).
e.g.
AddType application/x-httpd-php .php .phtml
Step 3.
The php file must be available somewhere that is addressable by Apache with a URI that starts http://. This either means that it must either exist in the DOCUMENTROOT directory or a subdirectory, or in an alias directory or subdirectory.
DOCUMENTROOT sets the default root location for all your html docs. So, http://localhost/ looks in DOCUMENTROOT.
I'm guessing that at the moment, the current documentroot setting in your httpd.conf file is the standard one for Windows.
e.g. DocumentRoot "C:/Program Files/Apache Group/Apache/htdocs".
If you wanted to have your own site, with it's own scripts etc, you can simply define an alias.
For example, if you wanted to have c:\webdata\mysite\ as the entry point to your site, with a subsequent sub-directory called scripts mapped to http://localhost/mysite/ you would need to add an alias line to httpd.conf.
It would like something like this:
Alias /mysite/ "C:/websdata/mysite/"
<Directory "C:/webshare/mysite/">
Options Indexes MultiViews
AllowOverride None
Order allow,deny
Allow from all
</Directory>
Then you could run you php scripts from anywhere under that , so the following 2 examples are both legal URIs
http://localhost/mysite/logon.php
http://localhost/mysite/scripts/logon.php
Sorry that's so wordy, but hope it helps.
Justin