openvpn bridge using NetBSD 4.0(i86) and XP?

[Carl Brewer <carl%bl.echidna.id.au@localhost>]

I'm looking to hook up a VOIP phone from a client's home to their work, 
at home they have a PC running XP hooked up to a generic DSL router 
doing NAT, and their work system has NetBSD 4.0 (i386) as their network 
gateway (also NAT'ing) and the PBX is inside their network.  The easiest 
way to do this that I can see is to use OpenVPN as an ethernet bridge, 
SIP's a terrible protocol to pass through firewalls etc, and I figure 
the simplest way (if not necessarily the most efficient) will be to 
bridge the network.

Before I go any further, has anyone here got anything similar actually 
working?  I've read this :

http://mail-index.netbsd.org/tech-net/2005/07/11/0007.html

And this :

http://mail-index.netbsd.org/netbsd-users/2006/06/27/0001.html

But they weren't terribly conclusive as to final success or not?  I need 
the setup to be "press a button" simple at the PC end to start and stop 
the link which is why I figured OpenVPN would be a good choice.

Any clues or pointers to more NetBSD-specific doco much appreciated, 
almost all the OpenVPN doco is loonucks-specific.

Thankyou,

Carl