Wasn't hard at all. Just buy the seperate parts for the halide: bulb, socket, wires, and ballast.
Grab a dremel and pop a few holes in the reflector to attach the socket, solder the wires together, and stick the bulb in and that's basically it.
Honestly though, I'm not totally happy with this fixture. This is mainly because I wish I could install an individual reflector for the halide independant from the PC lights.
The ballast is kept under the tank.