You can loop thru the elements in the WebBrowser.Document and if you find that it is an element of type INPUT, get its value (or whatever you want).

e.g.
(not tested code)
vb.net Code:
  1. For Each element As HtmlElement In WebBrowser1.Document.Body.All
  2.     If element.TagName = "input" Then
  3.         'you can access the element here
  4.         'e.g. we show its value in a messagebox for example
  5.         MessageBox.Show(element.GetAttribute("value"))
  6.     End If
  7. Next