Hey Topher,
I just joined the forum and saw your post. My wife has a 2005 SE that the head unit went out in. Just bought a double din unit from Crutchfied. If you go to their site and enter your vehicle info, they show exactly what you will need, including the steering wheel control harness. They send all the info you need to replace your unit if you buy it from them, including the required wiring harness (there's an additional charge for the steering wheel harness), faceplate trim kit and installation instructions specific to your year Xterra. If it's a 2005+ it's a snap, not sure about earlier models. One screw on top and everything else is snapped in to place with clips. Haven't installed mine yet do to time constraints but it should be soon and I don't for see any problems. Good luck.