Sorry for the delay in doing my writeup, I have been very busy.
MkIV Double DIN Radio Install (Sorry for the lack of pictures. I didn't have my camera when doing the install)
Note. These are the steps I took to install this stereo in my car and is quite involved, but does produce a beautiful finished product.
Install Items Used
- Z110BT 
- Metra trim kit http://www.metraonline.com/products.aspx?s=95-9012
- Canbus interface of your choice. I used http://pac-audio.com/productDetails.aspx?ProductId=278&CategoryID=26
- Euro antenna adapter for VW (Available at an audio installation shop
- Rear support stud bolt with 3/4 in rubber nub (ask at a audio installation shop; this is for rear support and is necessary with this kit
- Torx T20,
- Some type of plastic pry tool (I used one from Scosche)
- Euro radio removal keys (Available online)
- dremel tool or some cutting device
Instructions
Please follow the tutorials at the following 2 links. What you will be left with is the radio cage removed from the car.
http://forums.vwvortex.com/zerothread?id=958556
http://forums.vwvortex.com/zerothread?id=967146
Once the radio cage has been removed you need to make minor modifications to it to allow the harness plugs to fit without compromising the structural integrity of the cage. Start by installing the installation kit from Metra on the radio. Next test fit it into the radio cage and mark the back where radio cage interferes with the harness sockets. Take the radio back out of the radio cage (you will need to push down on the tabs on the top that are part of the Metra kit.
Next use a Dremel Tool or other suitable cutting tool and cut out the plastic from the back of the radio cage where you have marked it.
Next find the screw in stud and rubber nub you obtained from any audio installation shop and screw it into the back of the radio, top screw hole and then attached the rubber nub. This is going to act as vertical support to make the radio fit much more solidly. You will see that the rubber nub will fit into the pre-existing hole in the radio cage.
Next you will need to wire your radio harnesses up to the Canbus wiring kit following the instructions that came with it. It is important to note that since you have a MkIV safety brake status as well as backup sense will not be available, so you will need to wire these yourself. After taking apart the console in previous steps you will have perfect access to the safety brake switch. Just tap into that wire. As far as the reverse sense, on my car I wired this into the rear passenger side reverse light. It was the first wire in the connector in my car, but test each wire with a voltage tester and find the one that shows 12volts when reverse is engaged.
Next you will want to wire up the included GPS antenna or install a VW sharkfin which is beyond the scope of this howto. I will make a separate how to for this when I have a little more time, as it is very involved.
After the wiring is all done install the radio into the radio cage and then connect all of the wires to it. It is a good idea to not push the radio all the way in until you install all the harnesses, especially the iPod interface. Connect all wires up to the car and tuck them away under the radio behind the climate control. Test the radio function at this time. Reinstall everything back in reverse of the instructions above and when done you will have the best fitting double din you can have in a VW