Complex session issue

I have a situation where I have one browser window open for lets say web application 'x'. Now I want my user to goto application 'y' on the same domain in a new browser window by passing the authentication information from application 'x' to application 'y'. I obviously donot want my session variables to be continued in application 'y'. But at the same time I donot want to destroy the session of my application 'x' Since they r in two COMPLETELY separate browser windows, both sessions should logically be separate. But for some reason IE & netscape take a new window in the same Instance. Is there any way I can open a new browser instance, such that the same session is not continued and a new session in created leaving the old session as it is? Or is there any other work around for the same? - Divyank