I would get a motherboard and a separate video card. From the Adobe Website:
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.
Build looks good, you defiantly don't need a graphics to run CS5 well. I've seen plenty of people use just the integrated gpu would do. It's mostly reliant on CPU+RAM. The GPU of the i5 2400 would be sufficient especially since the iGPU can do all of those things.
Lol Photoshop doesn't need a CUDA enabled card to do it Jack. I'm using CS5 now and CUDA doesn't have a lot to offer from what I've read. Plus if you got a CUDA card you're looking at an extra $100 minimum to get a card that'd make a difference, that being the GTS 450. Even then you'd need to hack CS5 to enable it since the GTS 450 isn't supported.
But just to tell you OP the i5 2400 is good enough. You wouldn't even need the CUDA.