I downloaded AVG anti virus Free from download.com, and I have no idea how to install it once Ive downloaded it because it's a PHP file. Any help would be much appreciated.
The AVG Anti Virus installer could not be a PHP file. The PHP file could be an additional file included in a folder, but what you need to install should be a .exe (executable) file, for the installer to run. You do not need to run PHP files for installing AVG Anti Virus. But if you ever want to open a PHP file, use a plain text processor, like Notepad. If you want the PHP code to run, you need a server like Apache, configured for running PHP files.