How to make a CGI with C# ?

I want to create a CGI in C#. It should be started like this: I type the address to the browser, for example http://www.mysite.com/myservice.dll?somepage.htm. The service should read the contents of the HTML file, modify it and display the modified result to the browser screen.

I think this is a fairly easy thing to do, but I'm a 100% newbie to C#. Could someone show me an example or direct me to some tutorial?

Thanks, Csaba

You should have a look into the ASP.NET section. There you will find what you are looking for.
Through ASP.NET you can put C# - code into your html-pages and so you can make changes dynamically.