There are a number of ways to achieve this;
http://msdn.microsoft.com/en-us/magazine/cc300437.aspx[
^]
If you want it the easy and good way.
Try sessions and if not then cookies then viewstate and then url querystrings.
* Just go with sessions.
If you are well versed with php or jsp and html forms
Edit the 1st page form's action attribute to 2ndpage.aspx and in the 2nd page codebehind load event handler use the request object to get the POST data containing the values from the 1st registration form. Now write these values to hidden input html element or any hidden text box (do anything like this to preserver the data). Now edit the 2nd page form's action attribute to 3rdpage.aspx and just show all the data from the hidden textbox and the data from the fields of the 2nd page registration form to the user on this third page.
*U can use jquery serializetoarray or transform your your form data to json (GOOGLE for it) to convert your data to a more organized way which will help you save the data in the hidden field or hidden textbox more easily. This is an optional advice.
I hope I was able to solve your problem.
Watch my first article posted on codeproject and comment and vote:
http://www.codeproject.com/KB/HTML/speechinputapi.aspx
or http://blog.robinrizvi.info
Drop me a mail for any comments, suggestions or questions.