php and caching

Hi, I have a few pages on my site that contains dynamical content that must be "processed" each time the page is loaded. But I'd also want to allow the users to be able to use the back button of their browser to go back to forms and that these forms still contain the information they entered (instead of being cleared). Can someone give me a hint on how to accomplish this if there's a way to do it? Thanks, Alexandre Soares