any scripts for producing what's like in overstock.com (for multiple departmetns)?

Hello,
I'd appreciate if anyone knows or have any free scripts or script pointers that can produce the effect like http://www.overstock.com, which allows multiple departments each of which has different theme or contents... Customers once selected one department, he/she will stay with it throughout all the pages underneath this department, unless a different department tab is pressed.

I am developing an online store that will have at least two departments that carry different types of products.

The current website is built mainly HTML+Javascripts so I'd keep it this way. So I am looking a way to implement on the client side. I do have handful pages implemented in PHP (mainly for getting online requests and upload etc.).

Much thanks in advance.
Jason

If you're staying with Javascripting,
do a Google search for: javascript cookie tutorial

You'll need to retain the visitor's setting to keep them in the same department.

Please do not cross post. I've left the duplicate open (http://www.codingforums.com/showthread.php?t=76342), and closing this one.