[Using released NetBSD with a dynamic address]

You could always look at OpenVPN (pkgsrc/net/openvpn and 
pkgsrc/net/openvpn-current) which has performed brilliantly for me 
from NetBSD 1.6.2 onwards. You'll need newer NetBSD to us the bridging 
mode (tap driver), but routed works just fine. OpenVPN 2.0 can also push a 
majority of the settings down to the client (e.g. routing configurations). 
It even works through web proxies behind a very restrictive firewall.

N.B. I use it in TCP client/server mode; the peer-to-peer UDP mode seems a 
bit useless to me if you've got dynamic addresses and/or firewalls/NAT in 
the way.

-- 
Stephen