Is it possible the gauges were not accepted as "trusted"?

Other than that, I strongly recommend that you configure FSX to always "run as an administrator". This is how to do it in Windows 7, so I suspect that Vista will be similar. Navigate to [FSX root folder]\fsx.exe and right click on fsx.exe (you probably wont see the extension because Windows, by default, will have "Hide extensions for know file types" selected), select properties from the list that pops up, then select the Compatibility tab. Down near the bottom you should see Privilege Level. Now place a tick in the box beside "Run this program as an administrator".

Because you have FSX in the default C:\Program Files (x86), Vista is very protective of all the files store there (including all sub folders). IF you have FSX running with the administrative authority, it can do what it likes. If not, Vista will prevent it from doing some of the things it needs or has to do. This applies to ALL files that you are trying to install in C:\Program Files and C:\Program Files (x86). They MUST have administrative rights to make the changes required to make them work like they should. So always install FS add-ons with administrative rights.

Mark