Installing PHP on IIS 7 with Windows server 2008 can be tricky as the instructions mentioned in many official documents do not work with PHP 5.5.6. Here are the steps to install PHP 5.5.6 on Windows 2008 R2:

1. Download latest version of PHP from here: http://windows.php.net/download/ Make sure you download the non-thread safe version (nts) for IIS.

2. Unzip the downloaded file in a local folder, for eg: C:\PHP

3. Enable FastCGI on your server by following the instructions in this link: http://www.php.net/manual/en/install.windows.iis7.php

4. To connect with MS SQL Server 2008, download PHP SQL Server drivers (version 3.0) from here:http://www.microsoft.com/en-in/download/details.aspx?id=20098

5. Copy paste the downloaded files from step #4 to the /ext sub-directory in step #3, for eg: copy the files to C:\PHP\ext

6. Modify the PHP.ini file to add an entry to the extension, like: extension=php_sqlsrv_54_nts.dll

7. Download SQL Server 2012 client tools via this link: http://download.microsoft.com/download/F/E/D/FEDB200F-DE2A-46D8-B661-D019DFE9D470/ENU/x64/sqlncli.msi

8. Make sure that PHP SQL Server extension is enabled in IIS by going to IIS->PHP Manager->Enable disable extensions