Combine shipping and billing on same page

I have an oscommerce store with a custom checkout. The checkout is good because it has the "Easy Checkout a La Amazon" installed. It also has a custom modification ([login to view URL]) to allow the shopper to enter/change their shipping address ON the checkout_shipping page, without going to checkout_shipping_address. It also allows the customer to enter/change their billing address ON the checkout_billing page, without going to checkout_billing_address. I want to further improve the checkout by combining the checkout_shipping and checkout_billing onto the same page. You should look at the checkout that is currently on the site: [login to view URL] - you don't need to check out all the way to see how it currently works. It also needs to have a javascript where you click "billing address is the same as shipping" and it copies the information from the shipping part of the form to the billing part of the form. When I have chosen the bidder I will email the current custom files "checkout_shipping" and "checkout_billing". All work must be done and tested on your own server, I will install it on my server because I cannot allow outsiders access to my company's server.