I just installed a new headunit this evening. It's extremely easy. The hardest, most time consuming part is splicing the wires for the new headunit to the wiring harness, and that would probably be a breeze with a good crimping tool; my crimping tool is pretty cheap.
Take off the upper console (four philips screws), unbolt the stock radio (four hex head screws), and it pulls right out. Take the brackets of the stock radio and put them on the new one, connect the wiring harness, and reassemble. Piece of cake!