Defraggler had a little tool that shows the health of the HDD.
But I'm unsure what this all means. Could someone explain them, and which values are good and which are bad?
I found a wiki here: http://en.wikipedia.org/wiki/S.M.A.R.T.#Known_ATA_S.M.A.R.T._attributes
You will have to judge the values accordingly, relative to the HDD's specs.