The reason there are increasingly more multiple rail PSUs is because it provides for more stability since the different components that draw power from the 12v rails do so at different rates. The rails will allow for a "balancing" of the draw so as to guard (as much as it can) against a rail being overwhelmed and thus, shutting down the PSU. You'll find dual, triple, quad and now, even five 12v rail systems in most PSUs - all with varying degree of amperage like from 15 to 22 amps.
It might get confusing when you see something like "quad 12v rails at 17 amps per rail with a total of 60amps". The math doesn't quite add up but that is because the rails are rated to handle that much amperage (say 17 each) but the total amperage of the PSU is slightly less.
what does duel rail look like? the connectors? i have run a old 1.096ghz system for years and am now upgrading to a duel 2.4 pentium that im building myself and when i looked up the board on the net everybody was saying it needed a duel rail to run it, but i dont want to jump the gun and buy something i dont need, so what does the connectors look like? like how many pins and all that?
The insides of your power supply dont matter a bit. The wiring diagrams for the connectors are the same whether its a single rail or a 6 rail PSU so that any PSU with the appropriate connectors will work with any motherboard.
There are also many "dual 12 rail" PSUs that run both 12 volt rails off of the same regulated source, making them single rails that claim multiple rails because thats what the intel ATX spec suggests. Dont be fooled by marketing hype. Find actually reviews of the PSUs you are considering at sites like jonnyguru, also read through the PSU FAQ's at jonnyguru, they are very informative.