Right, so a number of people were interested in this one. There are already a few good threads on the topic, and I would say that this one was by far of the most help as I was doing this.For those who don't know, the adapter itself can be found here, and you'll need to go over to your dealership and probably have it ordered. I placed my order on Thursday, and picked it up Monday.
I have absolutely no idea if it will work for a non-Nav unit. Some said that if you have Satellite radio, it will work for you as well, but you lose the sat. I don't know for sure, so will not speculate.
A foreword on the difficulty of the install - it's not too bad... the second time you have to do it. Since you'll probably be doing it only once, the first time, expect to spend a few hours. I tried to take my time and do everything carefully, very often going back inside the house to look at the thread above. Overall it took just under 3 hours to do. If I had to do it again, it would take less than 1 now that I know exactly how things are put together. Depending on your experience with these things (mine just includes the same mod for my former 2004 Golf), you might be able to do it much quicker the first around.
4string did a good job pointing out the things to look for. I'll try to expand on them a bit more since sometimes the pictures don't quite do it.
So then... Step one - removing the diffuser control cover. This is where 4string's picture confused me a little bit, since this is the actual structure of the piece:
It's locked by the sides, so you don't want to pull it from the bottom, but instead you push one of the sides in and up like so:
That tool I'm using, btw, is something that's used for repairing laptops. Does a fine job without spending $20 on anything special. Unfortunately I have no idea where you might be able to get one, but if you google around for laptop repair tools, you might be able to find what you need.
Anyway, you have that thing removed:
Now you need to remove the grill. I found it easier to unlock one of the corners first, and then work your way around. Their locking mechanisms make it really easy to put back together, but rather scary pulling it apart (always afraid to brake one of the teeth off).
At the back you have you have this connector, which you just unplug after pushing in its sides:
And once you have the grill removed, it's time to move on to the piece underneath. Forgot to take the pic beforehand, but the place I've circled had a screw in it which has to go:
Once that screw is gone, the piece which was held by it can be pulled out in a similar manner as the grill. The only thing is that you should unlock the end of it first (side next to the windshield), tilt the piece towards you, and then pull it out.
Next piece is connected to the vents and that whole system. Start by removing these 2 screws:
Once those are gone, unhook the end and the sides like so:
I found removing the piece rather tricky, you just need to know which way to push/pull. I've labeled the general order of steps below. Unlike the other two pieces, once you've unhooked this one, you don't tilt it towards you, but instead away, and pull it out. Take a look at 4string's thread for a picture of the locks, you'll understand.
Now I found absolutely no need to disconnect the plugs on the back of that thing, just don't pull to far/hard and you're ok.
The next piece you have to be careful with, because it feels like it might just snap. The picture below shows all of its locks, so keep those in mind:
Finally you get to the nav unit. Just remove the screws and slide it out.
Before sliding it out, actually, might be a good idea to put your connector together. Very easy thing to do, and this is the first time that you actually need to look at the instructions. They label where each wire goes.
On the back of the nav, you find the following plug:
Again, use the instructions to connect everything properly. Be especially certain that you've pushed it all the way in. The first time I did it and tried to test it, I had only the left channel. Right one wasn't there because the plug wasn't all the way in.
Once you've done the testing and are sure that everything is working, you'll need to decide where to pull the cable out of. Below is what I went with. You can just as easily pull it to the glovebox. To make this task easier, find a strong piece of wire and push it through from the bottom. Once you found it, pull it out of the nav opening, use tape to attach the input plug, and pull the wire back. That is, don't try to just "throw" the wire in the approximate direction and try to fish it out. Much easier with something rigid that you can push through.
At this point my hands were too tired to hold the camera steady, so I didn't get any shots of putting things back together again, but this process took about 5 minutes and is much easier compared to pulling everything apart. Now the only thing left to do is just make sure that no extra parts were left after... the... ah damn it!!!
There is a general consensus that if you only have one screw left, it's not so bad. Troubles begin if you have two. At any rate, in my rush to put everything back together again (since it was getting dark as you can see), I forgot to put in the very first screw that you remove. I really didn't want any more rattle out of that area, so back I went...
Removing the grill this time took only a minute, so no big deal. Put the screw in, re-re-assembled the diffuser, and here we are with the finished product:
Yep, that's a quality iRiver player, not that crappy i... something... that everyone seems to have these days (j/k) 
No word on the quality yet, will let you know after my drive to the university tomorrow. The adapter in my Golf sounded absolutely horrible, to the point of just eliminating different frequency ranges. Honestly, if you were to listen to, I don't know, bohemian rhapsody you'd have no idea that the song began till piano started playing. Not volume either, just the frequencies were gone.
The next thing I have to do is find a good way of attaching the wire to the side so it doesn't lie there on the floor. That, however, is for the weekend.
Hope someone finds this info useful. If you have any questions, feel free to ask.
"Imagination is more important than knowledge. For knowledge is limited, whereas imagination embraces the entire world, stimulating progress, giving birth to evolution."
Plus it was fun taking apart my new car