A Dreambox (at least the one I have read about), refers to a satellite receiver that one can utilize to pick up FTA's. FTA is Free-To-Air television and radio channel transmissions. If you are in Canada or the U.S. you can find a list of those channels at FTAList.com
Technically speaking you need a satellite dish, a receiver (in this case the dreambox that you mentioned), and an LNB.
An LNB is a device that converts the satellite signal to a lower frequency band and sends them through the cable to the receiver. You can learn more about them at gosatellite.com