A part of the Technology Pack was SatNav and DAB. Changing the screen will not give you these features. You'd need to change the MIB unit in the glovebox. This would have to be done by a retrofitter. The screen is just a screen to display info on. A bit like a PlayStation and a TV, the PlayStation does all the work and the TV just displays it.
Saying that, I have seen on really early MK3's a screen and DIN unit all built into one.
Probably be easier if you can let people know what your current set up is, then they can advise further.