To tap into the power to run to your peripherals, you don't need to "splice" into the cables running to your motherboard. The power supply has molex power connectors that you can buy splitters for or make your own splitters (RatShack has these). Connect into them and run the proper voltage and ground wire to the screen (12v) and the USB hub (5v).
Now that I read emdzey01 post, he just said all this, but here's a pic...
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