WoW Model Viewer doesn't need to be installed.

1. Extract the downloaded file into a folder of your choice (i.e C:\Program Files\WoWModelViewer\).
2. Run WoWModelViewer.exe

If you encounter errors starting WoWModelViewer.exe (i.e. "this application has failed to start because the application configuration is incorrect")
please execute and install the vcredist_x86.exe provided with the download. Run WoWModelViewer.exe after completion.