A friend of mine's Apple laptop stopped booting. HDD issues. So he popped out the HDD and gave it to me to see if I could recover any files.
I've done this with PCs multiple times. Even if an HDD is broken to the point where you can't boot off of it, I have found that as long as the disk still spins you can usually recover some data.
So I popped this drive into an external enclosure. My PC recognizes it right away, but it can't actually read the disk, tells me it needs to be formatted. Is this due to the OS X filesystem (I am a complete Apple noob, I don't even know what file system OS X uses), and if so, is there a way to get around it?