This is the most painful as trying to get this to work is a pain the buttocks. Boot from the 360's OS, but do not erase anything (this is to make sure it works) Put the Xbox 360 Hard Drive with the other Hard Drive in your PC Take apart the 360 you have and locate the Hard Drive (this is the 3rd most painful step as some of the screws are exact fits and you prolly won't have the tools to do so buuut if you do the rest should be more or less simple. Imma still tell you (even though it worked by fluke, still pretty cool to learn )(also do not yell at me for capitalizing Hard Drive it is for reasons) I also will be doing 3 ways, hard way first, then the easiest also an oddly easy sounding one that almost never works for me. This is the way that worked once and it is semi-dangerous.
but it is lengthy and painful and did not even work for me.