vpn over natd

[Casey Scott]

Is it possible to configure natd to allow an ipsec client on a windows system  
to passthrough w/o modifying the packets? I need to have my cisco vpn client 
pass through my freebsd nat gw(ipfw firewall). I have seen in previous forum 
positing that there is/was a 'pptpalias x.x.x.x' parameter that is suppose to 
do this, but the natd on my system does not allow that parameter, its not 
available. 

TIA
Casey