I had covered previously how can you convert Windows Xp to look like Windows 7 here is how you can transform to make it look like MAC OS X.This could be achieved using Leopard X Theme pack which transforms Windows XP to Mac OS X. Thanks to DeviantArt user Vladimir0523 for uploading this.This comes with Leopard-X visual styles, styler, Mac search skin, Dock skins &  some Wallpapers too.If you wihs to change Vista to look then you can use a Transformation pack.

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Download Leopard X to transform Windows Xp to Mac OS X