STEP 1:
Download the latest PHP 5 installer (.msi) from:
http://www.php.net/downloads.php
Start the setup and click next.

STEP 2:
For webserver setup -> select Apache version which you have installed on your system , in my case its 2.2.x and then click next.

STEP 3:
Now to choose the Apache configuration directory click on browse and locate the configuration directory.
In my case its located at :
C:\Program Files\Apache Software Foundation\Apache2.2\conf.

STEP 4:
Under “choose items to install” :
Expand “Extentions” and select MySQL and MySQLi to install it on your HDD. You may also want to install PEAR and PHP manual under “Extras”(I recommend doing so). Click next and then install to complete the installation.

STEP 5:
Verifying PHP installation :

Open Apache service monitor and restart the service. It must now detect PHP. Now open the document root folder - the default folder is htdocs located inside apache installation dir. In my case its the default i.e. htdocs however you can change it by editing httpd.conf file. Now create a file named phpinfo.php. Open the file and copy paste the following code :

Save the file and open your web browser. Type in localhost/phpinfo.php and hit enter. If PHP 5 installtion was successful you would see all the details of the php configuration on your system.

STEP 6:
To enable MySQL support for PHP 5 :

By default MySQL is not enabled in PHP 5. In order to make PHP 5 access MySQL functions you need copy the file libmysql.dll to the system32 folder inside the windows installation folder. The dll file libmysql.dll will be present inside the PHP 5 install dir once PHP 5 is installed.

END…

If you are still confused or still facing some problem or have some questions/ suggestions fell free to reply!