Javascript ASP hidden form fields

I am writing a script that querys some asp pages and pulls some of the details from the webpages.
The problem I am having is that some of the details are on a 2nd page where you click on next to get to it.
However when you click on next it redirects to a default URL which uses variables passed from the previous page to display the relevant details.
What I need to know is the variables and there names which are being passed.
It may be the case that sessions are being used so it may not be possible to link directly to the next page.
The page also uses Javascript I have tried amending the CurrentPage variable in the URL but it makes no differneces.
Any help or advice would be apreciated the urls are below.

page 1 url
http://www.autotrader.com.au/dealerproducts/dealerProduct.asp?ProductID=S049&ProductTypeID=4&ProductName=Barry+Smith+Holden&SectionID=%2316&SubSectionID=%2316B&GroupID=&LocalAreas=&Regions=&State=NSW&Keywords=&OrderBy=Name&Site=AT&CurrentPage=20&SSSDescription=Sports+%26amp%3B+Performance

page 2 url
http://www.autotrader.com.au/dealerproducts/DealerProduct.asp

example: