I am not really an expert, I just borrowed the shit from the IT guy at work. Basically it just converts the multi-prong hard drive hookup to USB. There is also an external powersource that hooks into there but you can use one off of your computer. This is good if you have the shit, I have no idea on the price of this stuff.
Basically you just dont want to use that hd to boot. So if you have a desktop you can set the broken hard drive up as a slave drive then try to access it that way. I wouldn't recommend ripping apart an external housing.