My HDD crashed and won't be detected by a LiveCD. I think that my only solution would be to put the HDD into an external encloser, but I'm not sure. If I am, do I need an AC adapter & fan, what size & external interface?
You would not need an external enclosure. As long as you have one hard drive in the computer with an operating system on it, you should be able to hook up the other drive inside the computer as well. If it still does not detect it, you could try enclosing the bad hard drive in a freezer bag and setting it in the freezer over night then try hooking it up again.