I was trimming some wires off an old power supply for a lighting project I am making. I noticed that not all rails used the same guage of wire. This shouldn't be a problem for what I am making. I am planning on using five 20 Watt 12Volt ligh bulbs

You can shove one right into the 4 pin ATX motherboard power cable(it does bend the plug so you won't want to use it for your motherboard anymore).
I should take pictures and make a step by step on howto make hightech workbench lighting Red Green style.