Luna Element 5 is a Windows XP visual style based on the default theme Luna. The developer has modified it to add a few other touches of class but the basic outline is the Luna theme.
The combination is a little bit from the old Windows Vista GUI with a few additions from the new one. It's a nice combination of old and new and can be activated simply by selecting Display Properties, Appearance, Windows and Buttons.
There are four general visual styles to choose from namely, Blue, Blue Compact, Black and Black Compact. The compact options have been designed to optimize your desktop space. The disappointing thing is the resolution however - 800×600 pixels will definitely under use some of the capabilities of most modern monitors although it still doesn't look too bad.
If you're one of the many that don't like Vista but want a more elegant look for XP, then Luna Element could be your best bet.