使用WebBrowser控件,在documentComplete事件处理器里写

HtmlElement name = webBrowser1.Document.GetElementById("ctl00$content$loginname");

if (name != null)

    name.SetAttribute("value", User);

HtmlElement pass = webBrowser1.Document.GetElementById("ctl00$content$pwd");

if (pass != null)

    pass.SetAttribute("value", Password);

HtmlElement login = webBrowser1.Document.GetElementById("ctl00_content_summit");

if (login != null)

    login.InvokeMember("click");