The original guide is found at http://thoughtstorm.net/howto/bsdtopix.
Okay, I wrestled this for a few days; there is no real documentation on making a xBSD-based firewall talk the
VPN talk to a Cisco PIX that I could find. It’s based on racoon, with ipfilter doing the firewalling. gif interface support should already be compiled into the kernel unless you specifically removed it.