If the pump is not bad, there is no need to replace it. Just make darn sure that no dirt gets inside of the lines. Use a parts cleaner to clean off the line connections, before they are taken apart.
There is 3 bolts and the hose lines which need to be removed after removing fan belt
You can convert manual to power steering on a 1969 Camaro. the steering box will need to be changed, and a pump and brackets as well as fluid lines will need to be added.
The squealing could be that you need to add power steering fluid. Also you should check the belt that operates the power steering pump, if bad replace it. If the power steering pump is full and the belt is ok, then you may need to replace the power steering pump.
you will need a power steering pulley puller other than that its gravy
You NEED to replace the rack and pinion steering unit.
you might need to replace the steering rack
It's built into the power steering reservoir. To replace it you need to replace the whole reservoir. Fortunately, this is an inexpensive part... ($30).
You need to replace the power steering pump. If it is leaking, it is going out.
Replace the whole rack, it would take speical tools to replace seals
In order to replace a rack and pinion on a Nissan 200SX, you will need to remove the front wheels, the steering coupler, the power steering lines, and various bolts. You will then be able to remove the rack and pinion. Place the new rack and pinion in place, and return the various parts.
you will need a power steering seal replace.
Okay, I'm not sure which model you have but on some of them the power steering pump is actually part of the steering column. On these you need to remove the steering column to replace it. It's actually an electric pump rather than the traditional fluid pump under the hood.