What you'll need:
1) 2" black PVC elbow
2) 2" black PVC connecting ring
3) The boost gauge of your choice. Don't forget the vacuum line kit if you don't already have it !
4) Two (2) small screws to attach the PVC to the supplied aluminum guage bracket.
What you'll do:
I went with the VDO Vision series turbo gauge from 42 Draft Designs as it's a simple mechanical gauge, small, and you can change the lighting color to whatever you prefer with a simple bulb switch which are also available from them. As there were many mounting options it took me a couple of dry runs to find a final resting spot. I knew I didn't want a pillar pod, so the next logical place was to one side of the center cluster. Since the right side is where I mounted my IPod that was out of the question. The next logical place for a clear view (for me) was on the left. To mount the PVC to the dash I used the aluminum mounting bracket supplied with the VDO. The easiest way to do this is to drill holes on either side of the PVC as it faces you (like it were permanently mounted). Insert the aluminum bracket into the base of the PVC and adjust it (bend it) so it will be flush on the dash when finally attached. Mark screw spots throug the PVC onto the aluminum and then drill your holes in the bracket. Next attach the bracket to the dash with it's existing holes and supplied screws. I routed the vacuum line through the firewall and up through the dash about 1" from the main cluster. I routed the 12 volt switched and ground wires behind the main cluster and through the cluster housing. I used a rubber gromet to clean up the final look. To bring the vacuum line and wires into the PVC drill a hole at an angle just foreward (towards the windshield) of where the aluminum bracket will be. This should, if done correctly, reduce the likelyhood that the vacuum line will get pinched Not Good. Here you are drilling from the end where the PVC meets the dash as though the guage were faced away from you when finally mounted. All that is left after that is to attach the vacuum line and electrical wires to the pod and attach the PVC to the bracket. I still have yet to paint it, but so far it's a pretty good match to the existing console don't ya think?
Let me know if you have any other questions, and best of luck. For vacuum line attachment from the engine bay and the electrical connections (tapping the dimmer switch is the route I went and it's a piece of cake) do a search on the org. There are plenty of write-ups there. You can also go to VW Vortex.