For Windows 7 and Vista, the Windows Themes Installer is a featherweight freeware tool for changing themes without a hassle. It allows you to easily install the necessary theme files into their correct locations, without having to memorize or write down long file location strings. Users can change the .THEME file, EXPLORER.EXE, OOBEFLDR.DLL, EXPLORERFRAME.DLL, and SHELL32.DLL from the program interface, as well as remove or apply previously installed themes. When running it, you must Run as Administrator.
Though it's not hard to change themes, this app provides a good way to mix and match existing themes with your own creations. Windows Themes Installer doesn't come with a backup button, but it does have a default theme restore option. However, it's still a good idea to create a system restore before you muck around with system files. In short, Windows Themes Installer is a fun way to tweak the "clothes" of Windows Vista or Windows 7 without worrying about how to get things back to their standard wardrobe.