I was asked about this the other day when doing a presentation on Securing the Network Perimeter with ISA Server 2004 about how to configure VPN's. So I sat down this evening to write a step by step guide for you all. Then I remembered having seen a really useful guide recently. So instead of re-inventing the wheel, here it is: http://www.isaserver.org/articles/2004vpnserver.html
I would be very interested to find out if you have come across similarly useful guides and encourage you to share them with us all.
In the mean time, full credit for the article to Thomas Shinder and ISAServer.org for the article.
Enjoy! I know I did. Yeh OK, but I like this sort of thing.