You can do that using RASPPPOE on XP too, just create the extra WAN end-points, but what do you do after that? XP automatically takes the last connected connection as the gateway and routes all traffic using just that one connection. The rest sit there idle. That case you pointed out is one modem using one VPI/VCI, just using several WAN links over that same interface. You can't have multiple devices using the same interface though, it just will not work.