The vigor2710 will only support a single WAN IP address, but you probably only need one anyway. Having a fixed IP is better for security and also makes IPSEc easier to configure. The V2710 must be the dial out router. Your internal PC shouldn't need anything set on it for the VPN - i.e. it should stay on your private IP address. As Neal says, be sure your networks in each office are all on different private subnets.