you could always put a page inbetween the one that calls the form and the form itself with a redirect to the form - you'd ened to put it in the meta tags, and if anyone went back to the page they would be sent forward again to the form. However, they'd still eb able to click on the down arrow by "back" and select the page previously.
Alternatively, you could open the form in a new window with no navigation buttons - you'd need to do something like <a href="#" onClick='window.open ('./form.html', toolbar=0, status=0)'>Link to form</a> - they'd still be able to right click and then click on back though, so you'd need java script to stop them being able to right click.
Think the moral is that it may be possible to stop the casual browser, but be assured that if someone really wants to go back then tehy'll find a way.
