Why wouldn't you want the Back and Forward buttons to work? It's basic usability. Although your page is hiding and revealing content with scripting, to the user it will seem to be a conventional website where clicking the main menu loads a new page.
Let's say you want to show someone your 3D stuff. Is it more convenient and professional to give them a direct URL to that or to have to tell them to go to the site and click on a link in a dropdown menu?
Back/Forward, direct URLs and the redirection behaviour that you want for your form are all related and I doubt that you can have one without the other.
Good Point, I assume jQuery Hash change adds this functionality ?
Have you tried implementing jQuery hashchange event yet?
I will be, then I'll update