Folks who keep up with X-Plane are way past 5.66. This page is for those that have come across an old V5.x CD and would like to move to the last 5.x version.
This page describes changes specific to 5.66. Also see the Installating and Upgrading page for general information.
Some of the X-Plane mirror sites have 5.66. Try the following links (sites and contents come and go):
Only if you're at 5.60 or later. There is no mini-update for 5.54 and earlier. Way too much has changed to make a mini-update practical. The folder structure has changed and there are new planes.
The contents of the Additional Nav Data folder has been reorganized. Everything is now located in the Resources folder. Inside Resources, you'll find