There are many website which share beautiful themes for windows, of course Official Windows theme directory at windows.microsoft.com Host many of them. Some of themes are like windows 8, the way Desktop sceen is shown in Windows 8 and much more.
If you are not planning to upgrade to windows 8 than you may download these themes and make your desktop look like heaven.
you may check this site for downloading Windows 8 Transformation Pack --
www.thememypc.com/windows-8-transformation-pack-6-0/
You may also do same with Windows Xp. There are few themes available on internet which let you use your xp as windows 7 or vista. I personally have used them and they don't gibe any bug while running.
just Google "Transformation pack for windows xp/7 " it will have thousands of result waiting for you.
