Can be got from here

http://nts.wustl.edu/wireless/SSHSentinel1.3.2.2.exe

This one is free but the later versions cost. I have not tried it with
m0n0wall (or really anything else for that matter). It does however look
to be a lot easier to set up opposed to playing with Windows IPsec.
Comes with a firewall as well. 

Duncan