It depends on what you want to do.
Video cards only affect your 3D window.
RAM has a point of diminishing return (?!??!?) There is a point where after you have bought so much, buying more does not really help.
Neither has any direct effect on Photo-rendering. RAM would if you want to run other applications at the same time, but that's about it.
I would go for a faster processor first and foremost. Archicad's (and Lightworks') improvement is very nicely linear along that one...
Tom Waltz