Do this and it will save you a headache when you decide to install a after market deck in your car go to metra online or scosche and enter your vehicle year make and type. They will give you the dash kit, wiring harness, and antenna adaptor (if you need it). Order the right parts online or buy them from a local shop.
The kit will have instructions on how to take the factory radio out and how to put the new deck in.
FOR THE LOVE OF GOD DO NOT CUT YOUR FACTORY HARNESS OFF!!!! (if you do at least leave your self enough wire to reconnect it at some point if you need to) most cars harnesses can be purchased for around $20 USD. If your car requires a harness that costs more it's because your factory radio uses a data line and a aftermarket radio and some of the car functionality may not work correctly with out it.
Finally when it comes to hooking up your harness do not twist and tape the wires. Solder and heat shrink the wires or use a crimp to securely connect the wires.
Just a tip from a installer who is sick of fixing other people's hack job attempts at installing there own decks.