I have done this from scratch in a 3.0CS that did not have a/c. It is not for the faint of heart. It ain't rocket science, but it is a lot of work. If you look at it in bites, it's much easier to swallow. There are basically ten steps:
1) Choice of R12 (Freon) or R134a. This is the first step as it'll affect what compressor you buy (the fittings are different) and what lubricant you use in the system. If you're in a hot hot hot climate, stick with freon. It's still widely available.
2) Installation of new rotary-style compressor to block. Don't even think of using that old York piston compressor. You'll need the bracket folks are talking about. You'll also need to make sure your crankshaft pulley has a groove for the a/c belt. Don't take that for granted. Rare part for a tii, if I remember correctly.
3) Installation of condenser in front of radiator and electric fan in front of condenser. You can go with one from an '02 or retrofit the largest generic one you can stuff in there.
4) Installation of evaporator assembly inside car. I'd strongly recommend the Behr one for a factory look. I'd strongly recommend replacing the expansion valve while you have it out. Don't forget to verify there's a properly positioned hole on the transmission tunnel to drain it or else you'll have one smelly mildewed car right quick.
5) Installation of console around evaporator assembly. The non-a/c console has to be replaced. Again, the one that goes with the Behr system has the best factory look IMHO.
6) Drilling of holes through the nose and firewall to run the hoses. Scared yet? Those punches, the ones where you drill a small pilot hole then position the two halves of the punches on either side and ratchet them together, work great. Look at an existing a/c'd 02 for guidance on where the holes should go. Take photos and measure. Have a beer to help lower your blood pressure once you've done it. Paint the inside edges of the holes with Wurth zinc-rich primer or equivalent.
7) Fabrication of new hoses. If you can buy a whole a/c system out of a junked car, you can use the old hoses as templates, or you can have them all cut to length. There are very few shops here in Boston that do that kind of work (it doesn't get that hot here), but if you're in a hot climate, you should be able to find a shop who will cut each hose long, crimp one fitting on, thread it through, cut it to length, and crimp the other fitting on. If you're using R134A, you need new barrier hoses, but you'd be short-sighted not to use new hoses even if you're using Freon.
8) Installation of receiver/dryer on passenger side of engine compartment. Trivial. Again, look at an existing installation.
9) Wiring of compressor, fans, and switches. Fairly straightforward.
10) Adding of oil, evacuating, and charging it up. Utter joy when it blows cold.
Be aware that some of the newer compressors come without any kind of charging fittings on them (allowing them to be used for either R12 or R134a). That means that the fittings have to be elsewhere, like spliced into the hoses that plumb the compressor. If you don't do that, you'll have no way to get anything into the system. Ask me how I know... :^)
For all of these reasons, resurrecting a dead system is far easer than a from-scratch installation.
Good luck. It's a great project that enormously increases the enjoyment of the car by increasing the opportunities to drive it in comfort; at least that was my experience. Virtually all modern cars have a/c. We get spoiled. And it's not like it's sacrilege on a 2002; it was available.
--Rob