Remember what Microsoft said once about Vista's Aero theme and how it would be impossible to port to Windows XP?
[img options=nowrap,noborder]http://forums.blackravendragoons.com/filelib/2/thumb-screenshot_2009-04-17.png[/img]
The little window in the center is a Windows Presentation Foundation application using the integrated Aero theme that ships with Visual Studio. This is not a separately downloaded theme; it's a native Microsoft library running under Windows XP. Naturally, this is only the widgets, but they support all of the associated behaviors that Vista's widgets do (fading in/out, cycling of colors, etc). Now, I admit that this isn't the window manager itself, and while I understand the window manager exists in a DX-accelerated layer, I find it rather comical that at least the non-accelerate widget layer is portable to XP!
I guess it explains the various theme managers you can buy for XP that integrate similar styling to Vista!