AC compressor help!

I have a 1994 pontiac grand am 3.1l v6. my ac compressor needs to be replaced, the shop wants 350$ total with a 1yr on the rebuilt compressor. Now I have done work on my car before so I am thinking of doing this project myself over the weekend, but I have not messed with any pressurized systems before, so what would you advise me on doing? What should I becareful of if I decide to tackle this myself. I will have to go buy the proper tools for this project because I do not own any ac gauges or tools. I thank you for all the help you can give me in advance. I do have the Haynes manual for removing and installing compressor but it does not give me details about how to depressurize and so forth.