Switching to IPv6?

[FreeBSD Questions]

I've been considering switching my home network to IPv6.  I have a
computer acting as a firewall sitting between my ISP and my three LANs
at home.  Of course, my DSL provider gives me an IPv4 address, and
everything I want to access on the Internet is on an IPv4 network.
The whole point is to learn to set up IPv6, to play with IPv6, and to
become familiar with it, so when the day comes that the world actually
uses IPv6 (ha ha) I'm ready, armed with knowledge.

But the whole idea will go to pot if my firewall can't let my IPv6
networks access my IPv4 Internet connection.  Does FreeBSD 7 provide
such facilities as to allow access to an IPv4 network from an IPv6
network?  What will my Vista, XP, and FreeBSD clients do if they only
have an IPv6 address and I try to go to google.com or freebsd.org
which are on IPv4 networks?