I shall dissent from the earlier responses. I say, go for it, or at the very least research it thoroughly.
When I started looking at retro fitting aircon to my P1, I started a thread like this and got negative view albeit well intentioned. Now, when I get in the car, especially in the last week or so and feel that lovely cool air coming through the vents, I think to myself " I did that".
Having done similar things ( climate control and autodrop windows ), I would advise the following :
1. Research. Get a copy of a recent ePer - not the most recent as pud237 has said that they've now dropped the Spider. Version 67 is fairly recent and does contain Spider parts. Go through it and make a note of every part you need down to nuts, bolts & washers. Also work with the workshop manual - both the text and wiring diagrams ) as that will help tie things together. This will form your shopping list.
2. Sourcing the parts. I would recommend finding someone breaking a Lusso Spider and negotiate a price for every part you need. Then go along and strip the parts yourself. Take a roll or two of sandwich bags and put sub assemblies with their fixings ( nuts, bolts etc ) in bags and label them. Use lots
of bags to keep things separate. Use the wire ties to seal the bags to ensure everything stays together. As you remove things from the donor car, cross them off your shopping list.
3. Get the wiring from the donor car. It'll probably be easier to interface the P2 Lusso wiring to your car than starting afresh. Don't unplug the wiring from the donor car. Cut the wires so you have both sides of the connector(s). You can then rewire the cut side to join into your car.
4. Use the proper connectors to interface to your car. I can help you here with part numbers for the connectors, crimp terminals and where to get them and also advise on crimp pliers.
5. All the things I've done to my car are reversible. For example, I could strip out the climate control tomorrow and put it back to the basic heater and it would all plug together with the original connectors. There would just be a few additional connectors lying around.
6. Did I mention research? You really need to know exactly what you want as you don't want to miss anything from the donor car ( especially if you negotiate a price beforehand
). For example, on my aircon project, I knew the windscreen & face vent ducting was different on the P2 so I made sure I had them off the donor car. I would not have been able to refit the dashboard if I hadn't done the research to know I'd need those ducts. Even then, I missed the fact that I needed the P2 steering column support bar and that cost me a 160 mile trip! That was about the only parts error I made though.
7. Take a camera to the donor car and take photographs. Lots of photographs. Take photos of parts before and after removing them ( both the area of the car where they used to be and the parts before you bag them ).
8. Oh, and do plenty of research before you start!
There really is a lot of satisfaction to be had from this type of project. The first time you press that button and it all works as it is supposed to will make you feel really proud of what you've achieved. And pretty much every time afterwards as well. I do still watch my autodrop windows roll back up when I shut the door!
Hope that helps.