[procyon]

GPU does not accelerate photo editing. Mainly since photos are not 3D. For 2D you are unlikely to see any difference between different cards. Integrated will also do nicely (well I guess if you have a 30 inch monitor there could be some problems).
CPU and RAM are far far more important.
RAM is more important if you like to work on several 16-bit images simultaneously, with a bunch of other apps also in constant use.
CPU helps cut down batch processing time, and also makes the changes visible faster after you have tweaked some filter/raw converter parameters.
Also don't forget hard disk speed.
Photoshop likes to keep a lot on disk.
Also a fast disk makes the photos and software load much faster.