A WebBrowser control is just an embedded IE window and any/all settings in IE
are honored just the same including history.

If what you want to do is disable the back button then try the following
script in the head section of your pages

<script language="JavaScript">
<!--
 javascript:window.history.forward(1);
//-->
</script>

the above gets the job done more or less but its far from a perfect
solution. As far as i know you cannot disable the back button in IE but there
are ways to tricking it to act differently as by the script above.

Also see:
http://www.4guysfromrolla.com/webtech/111500-1.shtml
http://answers.google.com/answers/threadview?id=574062