Windows 7 RC is out and there are lot many customization and transformation packs available for Windows XP and Vista to convert the looks of them into Windows 7. Here are some transformation packs available to download for free which can convert the look and feel of your windows XP to make that similar to Windows 7.
Checkout the Screenshots of the Transformed Windows XP,
Windows XP Transformed into Windows 7
Customization Pack from Deviantart
Vienna 2.5 Transformation Pack
Download Windows 7 Transformation Pack – Vienna 2.5
HFN Windows 7 Transformation Pack
Download HFN Windows 7 Transformation Pack