Auto Install Feature for .PHP File - repost

We have an client based application built in Visual C# 2010. Periodically this .exe file automatically accesses a php file we have on our server. We want to provide our users with an auto install feature. It should automatically install a new .exe (software product) on our end user's machine. Completely silently and automatically. We need php code added to our existing php file to install a new .exe. Including error checking, accounting for UAC limitation, .etc. Anything that might prevent an auto silent install or cause our php file or .exe to "bomb". So, very basic php coding. Here is an example of what I'm looking for: //EXISTING PHP CODE //EXISTING PHP CODE //EXISTING PHP CODE //...ETC... // CODE BELOW IS YOUR PART //$Filetoinstall = '[login to view URL]'; //Check if $Filetoinstall is already installed on users machine //IF it is then do nothing //ELSE //Download file $Filetoinstall and execute it on end user's machine //Critical Points //1) Error handling must be enabled. If problem with this routine, remainder of .php file must still execute. //2) Must install "Software" silently. No prompts via web browser; UAC; .etc. Must occur without any notice or interaction with end user. //3) Must recognize and exit if "Software" is already installed. //4) This .php file gets called every 10 seconds. So any process that consumes time and/or resources is unacceptable. Code must execute quickly and not hang up rest of .php file. //EXISTING PHP CODE //EXISTING PHP CODE //EXISTING PHP CODE //...ETC...