Woah, if you are trying to run an internal drive through USB power you should think again.
USB is 5V only, and is very limited in the amperage they can provide per hub. They make products which allow you to have a SATA to USB adapter with a separate power chord like this one that I use (though I found mine on clearance for $5 (score!): http://www.newegg.com/Product/Product.aspx?Item=N82E16812232002
I don't know what he is trying to do. You can power internal devices with USB, but you'd have to combine multiple USB ports to get enough power. I know a lot of external HDDs now use 2 USB ports to provide up to 9W of power.