Windows 7 beta contains a new animated boot screen which shows animated items/balls that come together to form Windows logo.
If you want to enjoy the same boot screen in Windows XP or Vista, then here is a good news for you. "killer7ben" and "TSR-Pr" have created boot screens for Windows XP and Vista which look very similar to Windows 7 boot screen.
Windows 7 6956 Bootscreen by ~killer7ben on deviantART
You can download the boot screens using following links:
Download Windows 7 Beta Boot Screen for Windows XP
Download Windows 7 Beta Boot Screen for Windows Vista
You'll need "Tuneup Utilities" to apply these boot screens.
NOTE: The above boot screens are not animated.