PM Tom Hogarty writes,
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.
As Tom notes, a number of new features in CS6 (those relying on modern graphics hardware, such as 3D and the new Lighting Effects engine) already weren’t supported on XP.
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.