I needed support for a USB GPS cable, so I deinstalled Chart Navigator (Viewer) 5.07 and downloaded the 5.08 version on to my Vista Business machine and ran the GPSFIX program, following all of the Vista installation directions. The software runs fine, but Help/About shows that it is still version 5.07.0.0 and the GPS menu shows no options for a USB port. The GPS Setup Wizard is also disabled. The file I downloaded is named CHTNAV_ENGLISH.exe, of size 46.6 MB and was downloaded from http://www.maptech.com/support/doc.cfm?docid=123&CFID=3282742&CFTOKEN=47919607
Based on your posting, there are a couple of things going on. The 5.07 version of the software is the one that would have allowed you to connect to a USB GPS, however there were some flaws with the drivers that forced us to remove them from the 5.08 version. I just tried downloading and running the file straight from your link and it does appear that you got the 5.08 version. If you click Help-->About and look at the number printed in gold, just below the R in Navigator, I believe it will say 5.08 there.
So I think you do have the latest update, but that update actually removed, not added USB compatibility. The download GPSFix that you mentioned should return compatibility with those USB GPS, with the understanding that there are some flaws with those drivers that should be kept in mind while using that type of GPS. Once that is run, you can see those models at the end of the model list after clicking GPS>Setup, Manufacturer=Garmin.
I can't post pictures on this forum, but I'll send you an email that shows what I mean.
RE(2): CN (Viewer) version 5.08 download installs 5.07