2003 Lexus Is300 Headunit Installation

[DPLexus]

I have recently bought a 2003 Lexus IS300 and do not like the stock radio so I am replacing it with a Kenwood DDX418. Before I start cutting wires I have a couple of questions. First off when I bought the headunit, the salesman gave me an amp with it saying that it was an adapter for the stock amp... where and how do I deal with this? Also I would like to bypass the parking brake safety feature so I may play movies while driving... does anyone know the easiest way to do the bypass, I was not sure if I could ground the green wire straight to the ground wire or if I would have to do a relay setup. Anyone with experience with the bypass on this model headunit and Lexus would be greatly appreciated.