It turns out that the problem people are seeing with the OpenSceneryX installer is due to the security features in Vista (specifically, User Access Control or UAC). This means that a program cannot, by default, create files and folders in areas of your hard disk that Vista thinks it shouldn’t, which can include the “Custom Scenery” folder inside your X-Plane folder. Unfortunately, this causes something of a problem for a program that is meant to install files and folders in there, such as the OpenSceneryX installer.
While I work on a fix for this, my suggestion to all Vista users is to run the installer by right-clicking it and choosing “Run as administrator”. This gives it elevated privileges that means it can write to your X-Plane folder.