Form variables vs Sessions

I am having a problem with a form system that I am developing. It is a multi page form with over a hundred different possible variables. The problem that I'm having is that when a user enters invalid data on one page and then submits to the next page I want that page to go back to the previous page with the form fields already filled in. Currently I have the form going to the previous page with a custom error message, but am having a problem with getting the fields filled in. I pass the variables from page to page by using PHP to convert them to hidden form fields. I have considered using sessions but am concerned with the high overhead due to the number of variables. Any help with this problem would be greatly appreciated.Get more from the Web. FREE MSN Explorer download : http://explorer.msn.com