msdn.microsoft.com/.../con\
verttoaspnet.asp for asp3 to asp.NET

is a VB COM object to do the dirty work.

But it may be something similar between 2 .NET apps ?

there is another very simple version at gotdotnetusers but I don' know how
effective it is.

To tell th etruth I'd have guessed differently ... I'd hve thought it would be
to do with httphandlers, httpmodules and httpfactories. They are accessed
earlier in the pipeline than the actual app and are configured in web.config

Session is handled via a module (see machine.config) as are others.

To do what you desire I would have thought you could some httpmodule to get
underneath both your apps and hand them the same session  object or
httpcontext....

how exactly I simply couldn't tell you.

But thats the way I would have thought about it if I hadn't searched MSDN.

I have heard that you can do things like override the session handler, replace
it with a custom one, - if you can do that then surely you can send 2 apps he
same one.