IPCop and DynDNS behind NATing DSL modem

I'm trying to set up a VPN between two IPCop boxen. Fairly trivial,
usually. Both IPCops are connected to DSL (one home, one office), and
have dynamic IP addresses. No problem, DynDNS to the rescue.

DynDNS works fine on the home side, as the 'DSL gateway' gives the IPCop
box the public address. Not so at work. There, DSL is provided by an
ActionTec modem/router that does NAT to the (IPCop) local network. As
such, IPCop updates DynDNS with its private, non-routable address.
Little good that does me. :(

(FWIW, I already had a CIPE tunnel working before I had IPCops at each
end. Dynamic IPs was a problem though. Now that there is IPCop on both
ends, I'd like to use the DDNS and VPN capabilities of IPCop.)

Question is: what's the best way to get a VPN working in this situation?
Some answers that come to mind:

A1) a plain vanilla DSL modem that will give the (dynamic) public
address to IPCop's red interface.
KevinB, are you there? Are using the Cisco 67x I sold you? ;)

A2) a way to configure the ActionTec to do the same.
I'm not sure about the capabilities of this puppy. It has a bridging
mode. Can I use that with PPPoA and a dynamic WAN address?

A3) install a DynDNS client on a machine inside the LAN (or on the
IPCop) which will update DynDNS with the appropriate external IP
address, and configure ActionTec to be an end of the VPN tunnel (not
sure how that'd play w/ IPCop on the other end).

Any thoughts are (as always) greatly appreciated.

--
-Eric 'shubes'

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