C# windows application needs to send a string as a parameter to a webpage

I have a C# windows app that needs to do something like what I have in Javascript here:

$data_string = escape($data_string);            
submitdatawindow = window.open("http://www.somewebpage/submithere.php?data_string=" + $data_string);
submitdatawindow.close();

Basically I need to send a string like an HTML POST (with the escape function) to a web page.

Even better if someone can show me how to POST to a webpage from a C# windows application without actually having to open an IE browser.

Thanks, all