Disable Backspace to Previous Page

Hi,
I feel like I'm really close but yet so far away with this.  I have a form and when the user hits the backspace button when focused on the web browser I don't want it to go to the previous web page -- but I still need the backspace button to work in textboxes in the form.
I have a javascript function that appeared to work just fine:
<script type="text/javascript">
       if (typeof window.event != 'undefined')
           document.onkeydown = function() {
               if (event.srcElement.tagName.toUpperCase() != 'INPUT')
                   return (event.keyCode != 8);
           }
  &n ...