Hi folks. I gave up on the nay-sayers and did my own project. Requires no modification of VB pages, just a plugin.
http://nowonder.com
http://macosx.com
Share the same forum, you can login to one site, and if you use the top right link to the other site or any link that links directly to the other site without a redirect will keep your same session active.
This works on the same server, can be same or different ips, different servers and in my scenario it shares the same DB. No javascript used or issuing illegal cookies or quick/stupid redirects.
We provide high level forum integration between sites but comes at a fee. If you are interested in this, please IM me with your information and requirements. Everyone has unique needs so we customize solutions for your needs and let you know if its possible. (we don't listen to everyone else that say it isn't)
Scott