DHTML Popup Wanted

Hello I want a window to slide down on my site after 90 seconds The window will have a timer on it.. so the visitor can see it count down for 60 minutes After the time runs out the window closes and redirects to an "Offer Ended" page This will use cookies, so if the vistor leaves to go to another website and comes back later. The timer will continue to countdown. When they return after 10 minutes, the timer will show that 10 minutes has elapsed.