I don't think you can access ASP session data from anywhere other than an ASP within that application. You can't even share the data between websites on the same IIS server.

You could iterate through the Session collection, and save the data to disk or database before passing the user to the apache site. And just pass them over with a unique id that's difficult to guess - perhaps an MD5 hash of some sort. Then in the Apache application, query the database or file and read in the session data to your favorite Apache Session manager.

The problem is that if you pass the user back to the parent application, the Session might have expired by then, forcing the user to log in again. So you might need to increase the Session time in IIS. I would look in to whether it's possible to move your new application to IIS, or the original application to Apache - it might make things easier.