Eric,
Actually you can use any stateful VPN tunnel: OpenVPN, PPtP, L2TP, SSTP etc. OpenVPN is kind of complicated to set up (certifcates and other details).
The idea is to initiate the connection from the dynamic IP to a static IP, and reconnect on IP change from the new dynamc IP.
I personally favor PPtP or L2TP (optional with MPPE encryption), since this protocol is supported by almost any OS (Windows, Mac, Linux) and is light on the processor.
So, what you need is to set up a VPN server (e.g. pptpd) on a machine which has a static (or even dynamic) IP, which has a working IPIP setup. The ampr tunnel endpoint for the subnet in question has to registered to be the same as that of the VPN server (since the acces will be via that server).
From the VPN server, the ip frames for that subnet will be routed via your
VPN tunnel to reach the machines on that subnet. You have to treat the VPN link as a direct virtual network connection connection.
73, Marius, YO2LOJ