Install 7-Zip to extract Windows 7 themepack
Windows 7 themes use the .themepack extension which Windows XP and Windows Vista cannot understand. To extract the files from a downloaded Windows 7 theme just install the free 7-Zip utility that can handle the .themepack extension, and use it to extract your files to a folder on your PC. Remind that WinRar cannot handle .themepack extension. 7-Zip is a free and open source software.
For Windows Vista Users
If you are running Aero on your Windows vista, doubleclick the .theme file in the new folder you just created. This will change your windows border to the one in the new theme as well as your wallpaper to the default wallpaper in the theme, although this will disappear when you reboot so you will have to go to the theme folder. Then click on the wallpaper you want to use and select ‘set as Desktop Background’.
For Windows XP Users
XP doesn’t support Aero, so to set your wallpaper go to the theme folder. Then click on the wallpaper you want to use and select ‘set as Desktop Background’.
Create Windows 7 Desktop Slideshows
Neither Windows XP or Windows Vista support Windows 7 Desktop Slideshows so to rotate your need to install a tool to rotate your wallpapers. A good lightweight simple tool is the great Wallpaper Shifter app. This application picks a random wallpaper from a directory selected by the user and sets it as the active Windows wallpaper.
Download Wallpaper Shifter
Add Theme Sounds & Icons
Adding .themepack's sounds is a easy process. Just copy the sound files (.wav) to the default media folder C:\Windows\Media.
If you are using Windows Vista the theme file will automatically use these sounds
How to add windows 7 theme icons:
Right-click anywhere on the desktop, choose ‘Personalize’ and then ‘Change Desktop Icons’. Select the items you which to change, click ‘Change Icons’ and browse to the location of the new icons.
Right-click anywhere on the desktop, select ‘Properties’ and choose ‘Customize Desktop’ under the Desktop tab. Select the items you wish to change, click ‘Change Icon’ and browse to the location of the new icons.
Changing Screensavers and Cursors
If your Windows 7 theme includes a screensaver or a new cursor then just do the following:
Copy the screensaver files (.scr) into your Windows system folder usually located at C:\Windows\System32 to be able to access the new screensavers versions of Windows.
For cursors copy the Windows 7 cursor files (.cur or .ani) to C:\Windows\Cursors on XP or Vista, and then apply the new set using the mouse settings under Control Panel.
Thats All! Now you can easily use any Windows 7 themes to your Windows Xp or vista. So whats are you waiting for? Lets start now.