Photoshop CS5 and CS4 leverage the video adapter's chip (the graphics processing unit, or GPU) instead of the computer's main chip (CPU) to speed some functions. Photoshop accesses and uses the GPU when the GPU:
supports OpenGL, a software and hardware standard that accelerates video processing when working with large or complex images, including 3D.
has at least 256 MB of RAM.
has a display driver that supports OpenGL 2.0 and Shader Model 3.0, which the GPU uses to perform rendering effects.
I'd say the answer is: