Before replacing the compressor, did you verify it's really dead? Incorrect refrigerant level, contaminated refrigerant, faulty expansion valve, defective compressor clutch, etc., can disable the compressor. Compressor and other AC component replacement are best left to certified shops, unless you have the required equipment to perform the service. Your other option is to have the system evacuated at the shop and then you can work on it. That's the route I take when I need to replace AC component in my car. Remember, it is illegal to discharge refrigerant into the atmosphere.
If the compressor is really defective, it is advisable to replace the Receiver-Drier (a.k.a. Liquid Tank), too, as it can get saturated with water vapor once exposed to atmosphere. Before charging the system with refrigerant-oil, the system has to be evacuated again to remove residual contaminants.
Refer to the link below for more information on how to diagnose AC problem. Use AC Manifold Gauge to check low and high pressure of the compressor. It can be rented from car parts store (maybe free from Autozone).
http://www.nicoclub.com/FSM/maxima/1996/HA.pdf
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