I got a strange error when trying to install the KindlePreviewer application from Amazon.
Error: "KindlePreviewer instance is already running. Please close all KindlePreviewer Instances and press Retry to continue Installation."
I checked task manager and there were no running instances. I then realized that, like most of the install problems on Windows 7, this could probably be fixed by running the installer with administrative rights. Sure enough, right clicking and selecting "Run as administrator" fixed the issue.
I'm just posting this in case someone else forgets to run this as admin and searches for a solution. Hope I helped!