Would like to automate the download of a file from Web site. The download is done by a javascript__doPostBack function

I am a newbie in JScript and web programming. I have the need to periodically download a file from a Microsoft HLK site, and would like to automate this process. The download link within the page invokes a javascript doPostBack function. I have tried to execute this from a c# program by using the WebClient class and failed in executing the doPostBack function. Any ideas?