I'm trying to create something like a "child / modal window" that visitors can minimise and then use the information at the right time.

For example this page of my wordpress site http:// carp-fishing-reels. com/bite-alarms/
at the bottom of the left-hand side menu is a 'Discount Codes' tab which if clicked brings up a modal window (using facebox). Something like this that can be minimized and then restored for the discount code at the checkout, is what I'm aiming for but don't know what the possibilities are?