From http://gurusunleashed.com …toshop-and-windows-xp.php
The Photoshop team would like to provide advanced notice that Photoshop CS6 (13.0) will be the last major version of Photoshop to support Windows XP. (Photoshop CS6 does not support Windows Vista.) In addition, all subsequent Photoshop feature updates specifically for Creative Cloud members will no longer support Windows XP. Leveraging advances available on newer operating systems and hardware allows us to deliver significantly better performance, and focus our innovation efforts around the areas of the greatest benefit to our customers.
Photoshop CS6 already demonstrates that relying on a modern operating system, graphics cards/GPUs and graphics drivers can lead to substantial improvements in 3D, Blur Gallery and Lighting Effect features not available to Windows XP customers. The team hopes that by providing this information early it will help you understand our current decisions around operating system support and where we we’re headed with future releases of Photoshop. We encourage all customers who are currently using Windows XP to begin making their migration plans now so they can fully take advantage of future Photoshop innovations as soon as they are available.