...not sure anybody is around anymore, but here goes...
We have a VPN server running 10.4.11 server, and various and sundry mac clients from 10.4-10.7, and an iPhone client, but now we are trying to connect a windows 7 client and are at total fail -- there is no sign in the logs on the server that it is even getting a connection request. We have set the following things:
On the Options tab, un-tick "Include Windows logon domain"
On the Security tab,
set the "Type of VPN" as L2TP/IPSec
click on the "Advanced settings" and entered the auth key
set the encryption to "Optional Encryption"
selected "Allow these Protocols" and tried every permution of PAP on/off, CHAP on/off, and CHAPv2 on/off
On the Networking tab
under IPv4, hit Properties, then Advanced, and on the IPSettings un-tick the “Use default gateway on the remote network”
(basically selecting the win7 analog of the osx setting when we see it, then following various hints and instructions from googling around)