Wordpress Support

I have a html web page that i am using as a php template page. I need to be able to edit this page within the Wordpress backend, can this be done? Its crucial that the page loads in the backend just like when the page is viewed in a browser for ease of editing with all the css. I have tried this and the page loads in the backend but without the css and the layout.

I have watched this tutorial but the page wont load correctly in the backend!!

http://www.youtube.com/watch?v=1o2XcHqQbRY

basically what I need is to be shown how this is done, I am willing to pay the fee for who can do this properly.

Richard