I have it also!!!!
The cd goes into the boot fitted changer.
Good features of the unit are, the gps system very quickly picks up on alternative routes if you go wrong or decide you are not happy with the route it gives you. Another good feature is the menu system with places of interest ie airports, hospitals,town centre, etc. The mapping system is excellent with range down to 125yds up to I think 50miles.
Only downside is the map is out of date at the moment and I have found a few new roads that I use and i am travelling through fields. As yet I do not know of a new version yet and my 172 was registered in may 2002
Hope this helps