EVERYTHING IS OK!!!
I can't believe it, but after all i've worried about in the past 48 hours, and being such a royal pain in the *** to all of you - do you want to know what happened?
To begin with, I must have been extremely lucky that the other machine did indeed use SATA technology, despite being built around 4 years ago.
So I hooked up my hard drive, started the machine, and the first thing I was greeted with was a Windows screen strongly recommending that I perform a consistency check on one of the drives. So of course I went ahead with it (syscheck) - it found and deleted/replaced several indexes. I then went on into Windows, accessed my data and everything seemed absolutely fine!
Of course, my first action was to copy EVERYTHING onto my external hard drive, but nontheless i'm getting the feeling the drive may actually be "repaired" and safe to use again.
I think this is along the lines of what Mak213 was saying earlier. Presumably, the problem was very small, but the files that were affected were so fundamental to Windows boot sequence that it failed completely - could that be the case?
I have yet to try it again on my own machine, but i'm guessing it will be fine. What's important is that I have everything successfully copied!