I had a similar issue with a screenscraper program, and solved it with the following code:
HtmlElement element = Document.All["username"];
element = Document.All["password"];
element = Document.All["commit"];
The textboxes are named
in the DOM of the web page, and the action button is labelled
. You just need to look into the HTML source to find the names of the elements that you wish to alter or otherwise manipulate.