secure adhoc

[kalin m]

hi all...

i wrote this to the general questions list without much success. trying 
my luck here...

wondering if somebody has done vpn between a bsd box and a portable 
device running windows mobile. is it possible?
looking at the wireless networking off the handbook gives a direct 
example with 2 bsd machines.
the bsd machine and the wireless device are hooked up now adhoc. they 
always going to be close to each other and there is no need of 
infrastructure mode at present time.
if vpn is an overkill in this case what would be the best way to lock 
down the adhoc connection to be only between this two piers and isolate 
anybody else that wants to get on...

thanks