Modifying ATX Power Supply for 12v Power - Easiest Method?

I'm building a small box with toggle switches on it. I want each toggle switches to turn on something simple (mostly just LED lights). I was trying to think of how to power the box, and I thought about using an old atx case power supply since I've got an old computer I could pull it out of.

I'm seeking advice because I have no experience with wiring at all.. and I don't want to burn the house down. :)

If I jump the green and black wires on the motherboard plug so that I can turn on the supply, couldn't I just buy a simple molex Y-splitter and plug it into an available molex plug, and then cut the yellow and black wires and use those for the power and ground?

Here are the Y-splitters I'm referring to:

Cut off the plugs from the Y, and run the yellow and black wires to my switch and then run a power wire from the switch to the LED light or case fan or whatever I'm powering off of that switch.

The switches I'm using are 12v automotive toggle switches.

Would this provide the power I need? Would it be too much power? Should I put in an inline fuse or a ohm resistor or something to make it safer?

I appreciate any opinions.. I'm curious if anyone has ever used a molex plug in this kind of way and how it worked. :)

No need for the additional cable. Just cut the molex connector off one of the PSU cables and your good to go. The yellow is your 12V and the Red is your 5V. Check the site for Bench top power supply instructables. And you'll find all the information you need for converting an ATX PSU.