"Satukoro" @ DA has successfully ported Windows XP "Luna" theme to Windows 7 and it looks like following under Windows 7:
As you can see it looks great and provides same XP feeling in Windows 7.
You can download this theme using following link:
Download XP "Luna" Theme for Windows 7
More Info
For more information on how to use this theme, please visit following link:
How to use custom themes in windows?
