The adapter that connects from the stock HU plug to the aftermarket HU plug can be bought at walmart for 5 or 6 bucks, I'm sure its cheaper than crutchfield, but I can be wrong. As long as you get the right one, there is no need to cut stock wiring. The only thing you need to do is connect the adapter which has wires on one end to the wires on the harness and plug them in the appopriate places and you're set. As for deck installation, you might want to look up the link below and see if this is the right dash for you (click the picture) and if it is you can follow that guide.
The Install Doctor - The Do-It-Yourself Car Stereo Installation Resource