I have absolutely no idea how, but I've managed to get the hard drive to such a state that the entire file system is corrupt, and other PCs can't read it. To the best of my knowledge, I've done nothing to the file system between having it in this PC, putting it in mine and getting locked out of the recovery console, and then putting it back in here...there was no change made to the file system, but nothing recognises it. Even the Windows Recovery Install doesn't see a Windows install on the disc, and it needs to totally format it to get anywhere with it.
Also, as an added bonus on my lucky day, the backup hard drive has managed to lose a .dll file from the system32 folder, and now I can't get that one to work either (though I'm hoping I'll be able to get it back eventually, I'm off to try it now). I can't see any way out of this that doesn't involve me losing all my photos, recordings, etc etc...it's goodbye 120Gb of data, I think. Two hard drives corrupt, both running on the same hardware...maybe it's not a hard drive problem after all. Or maybe I'm just an idiot who kills everything he touches, I don't know. Either way, it's not good.
I'm looking at that link now dmpoole, I'm just not too optimistic about it doing anything if the whole file system is corrupt. I'll see what it does and maybe give it a go if it looks vaguely promising.