It is quite the undertaking, and if you're only *thinking* about doing it, then you shouldn't do it. You have to WANT it.
You need to R&R everything from the seats forward...the entire manual airbox (next to the firewall on the passenger side) has to be replaced with a Climatronic airbox. To get the airbox out, you have to have your A/C refrigerant drained (vacuumed, really). In addition, you have to run a whole harness' worth of wires from the dash area up through the rain tray into the engine compartment.
That said, I have to say it's not all *that* bad. It took me two eight-hour days to do the physical work, and I was working alone with only a *decent* mechanical skill level. But I also put in about three months of research with wiring diagrams before I felt ready to tackle the installation.
There are maybe six of us now who have done it. SVTWEB was the first, and he had it the toughest because, well, no one had done it before him, and he was working with a wiring harness that he extracted from a Climatronic car. Now you can buy the harness from kufatec.de for about $150 shipped from Germany. I used that harness, and so did pheller.
Phil's timelapse video on YouTube is a classic:
http://www.youtube.com/watch?v=fEVCcDwMj_o
--Chris
