in your httpd.conf file make sure you have the following (some settings may need to change depending on installation)
## Only check for the version of PHP you have dont copy the PHP 5 bit if your running php 4
# PHP 4
LoadModule php4_module "C:/php/php4apache.dll"
# PHP 5
LoadModule php5_module "C:/php/php5apache.dll"
#Now to parse .php
AddType application/x-httpd-php .php
Thats for the Apache ISAPI Module and Apache 1.3.x for Apache 2.0.x add 2 on the end of each e.g. php5apache2.dll
Once that is done restart the Apache Server and create a PHP info page
phpinfo.php
<?php phpinfo(); ?>
Copy it to your webroot directory e.g. c:\Program Files\Apache\htdocs (depending on your installation directory)
Then to access it
http://localhost/phpinfo.php
If your not sure what you web root is look for DocumentRoot