DSL VPN Tunneling without static IP's

I have a friend who wants a network set up. He has an office (main location), another office (remote location) that needs access to the main office, and he wants to connect from home to the main office. He wants it to be secure, so I figured a VPN would be best suited. I picked up 3 Linksys WRV54G dsl routers than can do VPN tunnels and VPN client access. I configured them with 3 local networks 192.168.161.0 (main office), 192.168.162.0 (second office), and 192.168.163.0 (home). All three have different DSL providers and modems, none of which have static IP address'  In this scenario, how do you config the VPN tunnels? Initially I set them up as routers with DHCP set to get the IP from the DSL provider, didn't work at all. Changed 1 to gateway instead and it allowed the site access the internet,didn't try a second one to connect to that one. In the configuration page you put the local network, the remote network, and the remote gateway addresses. Is the remote gateway address the ISP address that the DHCP picked up? If so, when the DSL bounces for some reason, you would have to manually have someone change it on both ends .... help