You'll need to read the install.txt file in the PHP directory to understand what all you will be doing to install PHP correctly.
First grab php.ini-recommended and rename it to php.ini, now move this file to your windows directory either WINNT\ or Windows\.
Second move the dlls that are in the PHP\dlls directory to a system folder either WINNT\system or Windows\system. Also, copy and paste php4ts.dll in this directory.
Add these lines to httpd.conf file
ScriptAlias /php/ "c:/php/"
AddType application/x-httpd-php .php
Action application/x-httpd-php "/php/php.exe"
Your apache main root should be in your Apache directory the root is called htdocs\. This is where you'll be placing test.php. Now in your browser call
http://localhost/test.php and see what comes up.
DON'T FORGET TO RESTART THE SERVER!