Basically, if you already have a double din head unit in the car (i.e. Symphony) then it is easy - as lon as you get the right unit from ebay (part number 8P0 035 192 I think). But if it's a single din HU you have (Concert or below), then you will need a new double din cage and climate control unit (as it will need to be lower down to accommodate the large HU), and it's not so simple.
A few people have done it on here, and if you look on the ICE forum section, I'm sure you will find a whole load of threads on the subject from the past. I think it is craigb on here that fits them.