the latest creative suite is shifting more and more workload over to the graphics card, so a decent graphics card can make a difference.
I had ( still have it in a box ) a nVidia GTX 260 card with 768Mb ( 768 is the min, but 1Gb recommended min ) of ram. With the CUDA hack, I got the benefits of the accelerated options in photoshop and after effects. All that being said, off loading to the graphics card does not benefit ALL aspects of the workload … there was a good article i read from adobe which explained that sometimes keeping work on the CPU was faster than offloading to the GPU.
I’ve since upgraded to a GTX 670 card. For my needs, photoshop, after effects and premiere, it handles files without hassle.
I agree with the other comments too, max out the RAM and let adobe use the bulk of it, get the system 64bit and use a seperate scratch disk. It just makes things move along quicker.