If you are Windows XP user then you might want to try Windows 7 transformation pack 2.0 for XP ,
this transformation Pack will convert your XP completely into Windows 7 Look. But if you are looking to get
only Windows 7 theme for Windows XP, you are in luck.Here is the Preview of this theme:

1.) Go to C:windows esources.
2.) Create a New Folder with Name "Logon” as C:windows esourceslogon.
3.) Now Navigate to Downloaded Logon Package, there is 2 options i.e widescreen & normal (Choose on your wish).
4.) Copy Setup.reg & LogonUI.exe to C:windows esourceslogon
5.) Once Copied, Click on Setup.reg to install the logon Screen.
Just Reboot or Log Off for take Effect!