PHP Questionnaire

I need a script that runs on PHP and MySQL. Visitors need to be able to answer a series of questions. The answer to each question will determine what the next question is. At the end of the line of questioning the visitor needs to be presented with a php include. the include file will change depending on what the last question was. I need to be able to change the questions, and the order of the questions from an admin panel. the script needs to be placed on a .php page, and run without refreshing the main page. It will need to be similar in look and feel to [login to view URL] If the visitor changes the answer to a previous question, the process needs to start again from that point.