As we know Windows 7 beta build has been released. Windows 7 contains a new GUI. New taskbar, new startmenu, new Explorer, etc. You can take a look at following review which includes almost all new features in Windows 7:
This theme "SevenVG" has been created for Windows XP users and it'll provide same Windows 7 look-n-feel in XP.
You can also visit following tutorial which describes all required steps to make XP look-a-like Windows 7. It covers the new Windows 7 Boot screen, login screen, theme and a few other GUI mods: