Basically to do it properly you have to have an ISP that supports Bonding, that way you have one IP and your ISP will sort out spliting the information up and sending it to you, all your router does is re-assemble it and forward it, hardly and different than a normal router.
You can do it without proper line bonding but your router needs to be more sophisticated to maximize usage. This set up appeals to me more anyway as I can have a dedicated line for servers and the other for home use, so my servers always have priority on a line.