With regards to your question: what are you trying to do?
Is it enough that the url in the address bar remains the same, but the actual page address changes but can be discovered by the user? If so you can use frames to hide the inner frame changes.
You may want to look at a
pattern called the Front Controller, related to the Model View Controller (MVC) pattern. If you distiguished each page using action parameters, the URL would be the same. You could POST the action for each page or use the session to maintain a workflow.
As I said, it would help to have more information.
Dave