Change Windows XP to Vista with Vistamizer.This is a free theme to transform Windows XP to Windows Vista. With Vistamizer, you can get 3D effects, Vista icons, and other cool windows Vista looks on your PC running windows xp.
What is good about this theme is it does not require any third-party libraries or external applications and it is a complete package by itself. It creates a Restore Point, before transforming Windows XP to Vista. This ensures a safe un-install to restore your PC to pre-installed state.
Vistamizer also give you complete control in determining the elements to be installed. The vista elements include graphical elements, Windows Vista Sidebar for XP, Toolbar Tool-tips, 3D effects for “Alt+Tab” Switches between running applications and more. Even if you select certain elements which are incompatible on your computer, Vistamizer is smart enough to skip them, thereby ensuring PC stability.
You can also try another free theme to transform XP to Windows 7.