Not sure if this applies to the Oldsmobile, but I think you have to buy the indash kit depending if your original radio is din 1/2 or 2din.
For the wiring harness, this is a good deal. I would assume if your car is a 2003, you have to tap into the ignition wire for the switched lead. I know the Grand Ams are like that.
http://www.ebay.com/itm/NEW-GM-4004-...a96173&vxp=mtr