Firstly ensure you have the requirements installed.
1. Install IIS Role
2. Install Web Platform Installer
3. Install PHP 5.4 (NOT PHP 5.5) and install MySQL 5.5, Ensure curl is enabled (I also enabled error reporting initially)
4. Install wincache if you like to speed up PHP pages also don’t forget to install ioncube loader WIndows 9 VC (NTS)
5. In the php.ini file ensure you add “zend_extension=c:\\Program Files(X86)\\PHP\\v5.3\\ext\\ioncubeloader.dll” – Use the double slashes
5. Install MYSQL Administrator or MYSQL Workbench on the server.
6. Create a database with a db user through MySQL Workbench which you will use to install WHMCS.
7. Download a copy of WHMCS and extract it to your chosen path and link the IIS site to it by going to advanced settings.
8. Once completed install it as per normal on the site.
9. Now for security I recommend placing a temp folder with folders downloads, attachments and templates_c before your root (www or wwwroot) folder.
10. Ensure the above folders are writable
11. Next edit your configuration.php file and change any paths that are like c:\Domains\hostking.co.za\wwwroot to something like c:\\Domains\\hostking.co.za\\wwwroot\\ etc. Use the double slashes is key to making it work properly.
12. If you’ve followed the above all should be working on WHMCS perfectly.
13. If you however try and login to admin area you will receive an error saying the custom folder specified is different. The fix of the init.php file needs to be downloaded and uploaded to your site via this link: http://forum.whmcs.com/showthread.php?93382