you could power them through a molex connector. But, unless you get 3.3 or 5 volt LED's (which I've never seen), you will need a resistor. After that I assume you can just daisy chain them 20 LED's shouldn't be too bad. In fact ... you could probably integrate a resistor into a switch then mount the switch in the front of your computer
I think i'm gonna do that to the power plugs, looks really cool, and if i got a thermal switch, i could make them turn on and off at different rates like christmas tree lights do.