http://msdn.microsoft.com/library/default.asp?url=/library/en-us/Dnaspp/html/aspnetmigrissues.asp?frame=trueSharing State Between ASP and ASP.NET
Another important thing to consider is that although your application can contain both ASP and ASP.NET pages, you cannot share state variables stored in the intrinsic Session or Application objects. You either need to duplicate this information in both systems or come up with a custom solution until your application is fully migrated. The bottom line is that if you have made little use of the Session and Application objects, you should be in good shape. If, on the other hand, you use these objects extensively, you will need to proceed with caution and perhaps come up with a custom short-term solution to sharing your state.
Упомянутые "custom solutions" встречаются, но, естественно, в виде коммерческих продуктов. Ради временной заплатки на несколько месяцев покупать их не хочется. При этом подробностей о том, как хранятся сессии в IIS (их хранение на удалённой машине и сериализацию в MS SQL Server не рассматриваем) и как до них добраться, пока не нашёл.
