Try this tutorial!

This code automates control over IE and firefox. Download the code to see how they do it.

Hope it helps

Here are some samples from code I've written to control IE, maybe it can help:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Threading;

//...

void SetField(WebBrowser wb, string formname, string fieldname, string fieldvalue) {
  HtmlElement f = wb.Document.Forms[formname].All[fieldname];
  f.SetAttribute("value", fieldvalue);
}

void SetRadio(WebBrowser wb, string formname, string fieldname, bool isChecked) {
  HtmlElement f = wb.Document.Forms[formname].All[fieldname];
  f.SetAttribute("checked", isChecked ? "True" : "False");
}

void SubmitForm(WebBrowser wb, string formname) {
  HtmlElement f = wb.Document.Forms[formname];
  f.InvokeMember("submit");
}

void ClickButtonAndWait(WebBrowser wb, string buttonname,int timeOut) {
  HtmlElement f = wb.Document.All[buttonname];
  webReady = false;
  f.InvokeMember("click");
  DateTime endTime = DateTime.Now.AddSeconds(timeOut);
  bool finished = false;
  while (!finished) {
    if (webReady)
      finished = true;
    Application.DoEvents();
    if (aborted)
      throw new EUserAborted();
    Thread.Sleep(50);
    if ((timeOut != 0) && (DateTime.Now>endTime)) {
      finished = true;
    }
  }
}

void ClickButtonAndWait(WebBrowser wb, string buttonname) {
  ClickButtonAndWait(wb, buttonname, 0);
}

void Navigate(string url,int timeOut) {
  webReady = false;
  webBrowser1.Navigate(url);
  DateTime endTime = DateTime.Now.AddSeconds(timeOut);
  bool finished = false;
  while (!finished) {
    if (webReady)
      finished = true;
    Application.DoEvents();
    if (aborted)
      throw new EUserAborted();
    Thread.Sleep(50);
    if ((timeOut != 0) && (DateTime.Now > endTime)) {
      finished = true;
    }
  }
}

private void webBrowser1_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e) {
  webReady = true;
}