Fitting A Navigation Plus Sat Nav

I was wondering whats involved in fitting a Navigation Plus sat nav to my car, if it is at all possible, my car did not have a sat nav fitted as original equipment, but it does have the GPS aerial on the boot lid, also it does not have an option for sat nav on the menu control under the flap, I understand this unit is old technology but it would be ok for my needs if it could be fitted without too much work.