Hi. I think Richard is on the right track here. Either in the page header (under page settings in DNN) or within the initial JavaScript you could check the cookie value and then do the redirect as Richard suggested. I don't really think you would need to use Dynamic Forms tokens but its possible...
I would check this out:
http://www.w3schools.com/JS/js_cookies.asp And look at the function to get a cookie. You could include that in the custom javascript file or just use the logic and then use the window.location that richard posted.
Just an FYI on $(Tokens)... basically Dynamic Forms just replaces $(ShortField) with the value of that field, and it just replaces $(ShortField_FieldID) with the actual HTML field ID... so, its not really magic... Just JavaScript going on here which can be frustrating sometimes because it is case sensitive and although very powerful its basically its own programming language. If you do run into problems I would download FireBug for FireFox, its an app that we use here all of the time when working on client side events.
-Chad