This is possible. It is even legal to sell these descramblers in some states. It is the act of using this descrabler that is illegal. It's basicly stealing cable.
I'm not an expert on the subject, but I did some reading once. I do know that the cable companies have a few different signals that they use for cable TV. Therefore a different circuit is needed for the type of signal that is incomming. Also, at least in Arizona, the cable companies have a way to find out if someone is stealing cable TV. They're prosecuting people left and right around here.
My opinion, save yourself the time and energy.