You have a couple options... if it's nothing too large scale, you could do hidden form elements.
on your 2nd page, you could have it like so:
Obviously the HTML styling is missing from the above, but you get the point

When the user submits this page, the new information is submitted as well as the hidden fields containing the previous page info.
If you have a lot more information to collect or a lot of pages, you might be better off using sessions.
Here's a good tutorial on those:
http://www.tizag.com/phpT/phpsessions.php