I've read differing views on dual core processors. They SEEM to offer good speeds, but if the software isn't written for multi threading then often a faster single core will give better results.
As for the balance of sys ram and video ram, if the most intensive stuff you will be doing is photoshopping (and there's photoshopping and photoshopping, depends if you'll be doing heavy stuff like rendering or just a little touching up) then I would suggest the higher video ram would pay off, as it doesn't require the passing of data along the FSB between RAM and the vid card, can save processor cycles too.