Set up multi-site VPN connection

This is just a simple test project. I need help with setting up with a VPN connection/routing between multiple sites, where all sites must be able to communicate with each other. See attached drawing. Accomplished at the moment: PPTP VPN client in DD-WRT router location A connects succesfully to PPTP VPN server at home office. PPTP VPN client in DD-WRT router location B connects succesfully to PPTP VPN server at home office. Both locations A and B have full access to all resources at the LAN side at the home office through de VPN tunnels. Left to accomplish: All PLC's at location A and B should be reachable from the computer at the home office. PLC1 and PLC 2 both should be able to reach PLC3 and vice versa. So basically routing should be accomplished between the three subnets ([login to view URL], [login to view URL] and [login to view URL]). I assume some static routing tables or some such needed at all three routers. I am aware everything will have to pass the home router (the hub?), also whatever needs to go from location A to location B (or vive versa). Throughput should not be an issue as the amount of data can comfortably be passed along an ancient dial-up line :-) Security is not an issue, initialliy it's keep it simple, if this set-up can be succesfully tested we can in a later stage move to openVPN or some such.