I am indebted to you once again SD! According to my friend Speccy, what it has is "SATA Type, SATA-1 with firmware version 892C".
If the idea that the error which started this off may be down to a dying HDD is not off the wall - mind you, I've read of all sorts of other possibilities - then it may make sense to get my hands on a significantly larger drive. One might say that, whether it fixes the original problem or not, the current one is full-ish and needs replaced for that alone. Should it not fix the freezing problem then it will always be useful and it has the plus point of being cheap and diy-able.
Is there a reasonable chance that it might fix the freezing, now that we've looked at a few other possible explanations of the fault with no luck so far, or are the chances vanishingly small?