My ac compressor is squeeling like crazy. Its probably just the clutch assembly, but I've already got a cheap used compressor on the way.
How much of the work can I expect to get done myself, without having any kind of special ac equipment or knowledge about ac stuff?
I'd like to just slap on a new compressor, belts, and have the system refilled.
What else do I need to know?

The system has to be properly discharged before any work is done, you don't just open it up and let all the refrigerant escape. It is illegal to do so (yes even with R134) and also dangerous as the refrigerant is under high pressure and cold enough to result in instant frostbite with skin contact, and instant blindness with eye contact.
You should have a shop with the proper equipment discharge the system for you, and then go back after you swap the compressor for them to evacuate it and refill. They will also make sure the pressures are correct.
When replacing a major component such as the compressor it is also necessary to add the proper amount of oil into the refrigerant to replace what is lost when the old component is removed. Also you might want to have the shop check out that "cheap used" compressor before you install it, to be sure it is in good functioning condition and not filled with metal bits that will contaminate the system.

Clutch components can be replaced w/o removing the compressor. You can try that, if you're sure it's the clutch.

thanks