Sorry David, didn't realise you were talking about the 8P. As Paul said earlier, i'd get an Audi dealer to give you a demo - as far as I know the satnav should be the same in all the new models.
Jazz, Yes the audi satnav does display directions in the DIS. Fortunatly I managed to find an S3 that already had the satnav/tv fitted so I dont know exactly whats involved in doing a retro fit, I think theres some posts on it on here or maybe audi-sport.net. People seem to say that the aftermarket units (tomtom etc) are better than the audi satnav and a lot cheaper, but obviously the installation isn't as tidy as an OEM unit.
If you haven't found an S3 yet and really want the satnav I'd be tempted to hunt around for one thats already got it fitted, I doubt it will put the asking price up by as much as its going to cost you to do a retro fit.
Theres some audi satnav info here http://www.nav-plus.com/instructions/ - i think its an american site so there wont be anything on the a3/s3