IPSEC Tunnel Routing question

[Tom Thompson]

I would like to route all traffic over a gif/ipsec tunnel

I have the following situation
Existing internet connection in building A
Building to building wireless(between building A and Building B)

To secure the traffic going across the wireless I would like to run an 
ipsec tunnel between freebsd 5.1 based machines sitting at Building A 
and Building B.  I have the tunnels up and running but I am experiencing 
a problem with routing.  Building B does not have an internet connection 
so it needs to use the internet connection at Building A.

To lay it out in more details
Router at building A connections to the internet
FreeBSD 5.1 machine at Building A connects to router and to wireless bridges
FreeBSD 5.1 machine at Building B connects to Wireless bridges and internal network

What do I need to do you get traffic to flow from Building B to 
Building A and out A's internet connection?

I have tried setting building B defaultrouter to building A internal address(other side of GIF tunnel)

Thanks
Tom