very difficult, they are very different programming models and run in different processes, consider to write your own session management system, seeQ: Can I share session state between ASP.NET and ASP pages?
http://www.eggheadcafe.com/articles/20021016.asp
http://www.eggheadcafe.com/articles/20021016.asp
How to Share Session State Between Classic ASP and ASP.NET:
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnaspp/html/converttoaspnet.asp