DoctorJ, I have a 2002 VW Passat and one of my friends has a '99 Beatle. In both cases, as well as a few others I know of, they have been ‘pre-wired’ for a VW factory changer in the trunk. I don’t know if this is true for the Cabrio or not. But you might want to check and see before you make any plans. I know a lot of the recent VWs are pre-wired and the factory radio can control a changer.
If your car is pre-wired, installation is incredibly easy. You just mount the thing in the trunk (2 or 4 screws and maybe a bracket, depending on the car), and plug in the wires. My friend with the Beatle had the dealership install hers, and they charged $30. I got an aftermarket headunit for my car (so I can play MP3s), so I didn’t install the changer in mine.
The downside to this set-up is that you have fewer options as to which cd changer you would get. If you are planning to keep the factory radio, then you are stuck with either the factory VW changer or certain aftermarket changers with an adapter to make them work. Of course, the VW changer costs significantly more than most aftermarket ones. However, you can sometimes find them on Ebay. Also, the price of some of the aftermarket changers plus adapter is less than the VW changer.
If you want to keep the factory radio and your car is pre-wired, I’d recommend you try to find a good deal on the VW changer. If you can’t find a good enough deal, look for a Panasonic changer plus adapter. Either way, you can probably install it yourself in a few minutes.
If you plan to change the factory radio, you will have to get a changer that is compatible. In this case, the changer itself might be less expensive, but you’d have to run new wires. So the installation would be more involved and you might not want to do it yourself.
Yet another option would be an RF changer. These send an FM signal with the music, so you don’t have to wire the changer to your radio, you just tune into the right FM frequency. Installation is simpler, although you might still have to run power cables. The downside to this is that you have to have a separate controller for the changer and the sound quality is degraded somewhat. I’m not a big fan of these setups, but they work well for some people.