Ok...so it sounds like, if its just 2D pictures I am editing, etc, it places all of the data in the system RAM. But it will ONLY use the GPU memory if PSP is using Open GL or D3D, or Shader 3.0 etc. effects in PSP. I'm not doing any high end 3D graphics in PSP, so it sounds like I shouldn't shoot for the moon and get crazy on the feature set.
1. Given that I prob won't use Open GL or Shaders, etc will 512MB on-board memory suffice?
2. Does the memory bandwidth still count? i.e. 128-bit memory vs. 64-Bit memory bus. If I'm really just doing 2D work, does this matter?
I'd get a geforce 9600 level card with 512MB memory. This way you're covered if Adobe ever supports OpenCL, plus the really low level cards just suck. (only ATI cards in the 48xx series and 5000 series support OpenCL, meaning you'd need at least a 4850, which go for around $100)
BTW, there's 3 different levels of CUDA devices, that basically equate to Geforce 8000/9000 series, GT200 series, and Fermi. Something compiled in C for CUDA for Fermi may not run on a geforce 9 series card, though I'd imagine no one could exclude older CUDA cards if they can avoid it. (though nvidia did with some of their cuda and physx demos)