Graphics card will make the editing of highpoly meshes faster and smoother in running terms, since it’s realtime . I think that ram will help in this too, because it’s data, at least when you load the blend-file.
CPU will also do work when you edit or change the view mode from texturemode to shaded mode and that stuff.
Rendering only takes cpu and ram. The rendering is done by the cpu, but the data that comes from the objects to the renderer requires ram, so if you’re rendering a big scene, ram is also needed.
So, as theeth said, rendering doesn’t concern the gfx card. Unless you render in openGL mode in the game-engine. If it isnt real time, it doesnt concernt the graphics card.