I have completed this conversion, and a couple of other members on here as well.
Wiring up is simple enough (Though you can get Series I to Series II conversion wiring kits to make things easier).
The hardest part is programming the IQ unit to work with your car. (You will need the VIN number of your car programmed to the IQ unit to get it working)
A member on here DoubleDip from Ultimate Conversion Wiring can supply the wiring adaptor, the IQ unit, and most importantly the programming to get it all running.
(Though if you source the IQ unit and triim bits yourself, you can still get DoubleDip to program theIQ unit for you).
Also if you want Sat Nav, you may want to upgrade your cluster to a series II model later down the track (as the Sat Nav, traffic and speed alerts will not function correctly on a Series I cluster).
This is my install (Its changed a little bit since this pic, as I have fitted a Series II cluster since this)
DoubleDip programmed both the IQ unit, and the new cluster to work together, with my cars VIN number (As well as enabled the camera, Video Inputs, and some other fun stuff).
I hope this helps