You need a standard CAT5 (Twisted Pair) cable for each Cube and a hub (switch)/router. The broadband adapter is a network card, you just plug your cable into it, the other end into ANY (non-uplink) port of your hub and you're set. You can just look up how LANs work with PCs, just instead of PCs you connect Cubes to the net.
If you have only two cubes you can use a crossover cable instead of two TP-cables + a hub, the crossover cable connects directly between both Cubes.