how i can do that

I am intended to develop a windows application that enable user to connect to the internet and do control on some properties such as connection time, download, and site access. In my application I want a .NET code enable me to prevent user from downloading files or images with a specified extentions that I determine it in my database. I want C# code that can catch the connection. I want C# code that can catch the download. I want C# code that can catch the stream from internet. I want C# code that can catch the change in my desk space due to downloading. If one can help me? If one can consult to me? Thank you