I am in the same situation, it is not working, despite having precisely followed the instructions.
I have looked on the Internet for some help, and found this: http://www.isaserver.org/tutorials/...PN-Server-Using-ISA-2006-Firewalls-Part1.html
It is another page explaining how to configure VPN... the VPN server installation described is completely different from the one described in this thread.
Why ? Does it mean the server configuration in this thread is incorrect ?