In my 02 it's a piece of cake. There's just 6 screws holding the factory HU in, then I took the brackets off the sides of the factory HU and put them on the aftermarket one.
One thing you will want is a wiring harness to plug into your car's factory wiring(I got one on ebay for less than $3). Then you pretty much just match up the colors on the wires. And you should mount the ground wire to something solid inside the dash that's attached to the frame of the car. Do not run the ground into the factory ground wire on the harness, as it is ran for who knows how long, side by side with power wires.