If the data is textual in nature, you can add it as request parameters to the URL of the popup. Otherwise, you might consider storing it in the session so that it also available to the request that's building the page for the popup. Be sure to remove it from the session when no longer needed.
Another possibility is to have each JSP fetch the data using the same back-end mechanism rather than any "passing" of data. That's the way that I would approach it. I always view a JSP as a dead-end and not a source of data. [ September 06, 2008: Message edited by: Bear Bibeault ]