Verify that the junction works by creating a small text file in E:\Win7-Junctions\Installer and seeing it materializing in C:\Windows\Installer as well.
Cut-paste from Windows Explorer should be enough to move the installer folder. E:\Win7-Junctions, so the new path will be E:\Win7-Junctions\Installer. For convenience, it's better to create a subfolder to gather all the future junctions in one place, e.g. Take ownership of installer directory and all its files: takeown /f 'C:\Windows\Installer'
