Hi, confused newbie alert

I've just upgraded to an 8800GTX and am thinking I need a PSU aswell. I've read the FAQ at the top but there is more that I cannot get my head round.

To cut to the chase, I was going for a Silverstone ST85F or the Etasis ET850. From the recommended list i can see that they are both Etasis units so the cheaper of the two is the way to go............but, I suddenly found myself getting bogged down with whether i need 4 x 12v rails or just 2. I'm not too bothered about SLI atm and was going for the Silverstone unit as it has two 35amp rails as against the Etasis unit that has four but of lower amperage. I really would prefer the Silverstone unit as i already have a Jeantech 600w item that has 2x12v @ 19 amps each but does seem to struggle with my C2D cpu, P5B Dlx mbd and 8800GTX together.
Also, I seem to be unable to decipher what rail is connected to which part of the system. How do you know if 12v1 is only for the mbd or includes PCIe or has the cpu on it also or is that on 12v2.........very confusing.
Is there a standard that has to be followed or are all manufacturers at liberty to do as they please. I had to open the Jeantech and follow the cables to get some idea what went where but even that was haphazard at best.

Sorry if i have missed something in the forum.