I’m working on a major ASP to ASP.Net conversion project that can only really be done one page at a time. One of the obstacles to doing it this way was sharing session variables between ASP and ASP.Net pages.
Most solutions to this common problem involve intermediary pages that write the session variables of one type into form variables and then from form variables back into session variables of the other type (See Peter A. Bromberg’s example on eggheadcafe.com).
Microsoft’s Billy Yuen’s solution uses SQL Server as a repository for session data, and provides custom objects for both ASP and ASP.Net to access the session data.
Ultimately, we abandoned this since the site’s use of session variables was minimal and there were other ways of solving the problems we were using session state for.