How would a low power SLI config affect a dual rail PSU?

[peterson]

Let's say i was to buy a SLI motherboard and 2 nVidia 7600GT for a SLI configuration. These have their power fed through the PCI-E slot, right?
What if they are powered by a, by these days, standard dual or multi rail PSU.
Will the graphics cards and the CPU use the power from the same 12V rail?

Or is this where the extra molex connector at the motherboard kicks in?

Not that i think i'd ever spend money on SLI, but it made me wonder.
And shouldn't SLI require 3 12V rails? 1 for CPU and 1 for each GPU?

Or am i just typing nonsense.