identify not only browser, but even browser windows with session

hi, does anybody know how I could identify the browser window? my problem is, that i have a application framework and I want to use multiple windows providing different GUIs. Each window should be able to send a request and send a proper session key or unique key which identifies the application window. I cannot use get/post parameters, because the framework works in a different way and uses the path info. i also don't want to use the path info to pass through the window key. can cookies be stored for single browser instances (windows)? does the browser send some information that could be uses? thanks in advance, dorgon