If you installed on Windows XP, then it is expected to not have the 3D menu item or feature set. You may also have bought Ps CS6 instead of Ps CS6 Extended.
Regardless of having PS CS 6 Extended or Standard version, on Win XP, 3D options and some GPU enabled features are not available.
Please check this : http://www.adobe.com/products/photoshopextended/tech-specs.html
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