[IngloriusBasterd]

Well, I managed to sort my problem out - every answer I could find for the error I was getting suggested that either the registry or hard drive on my machine was to blame - and then as an afterthought they generally said that it was also possible the file was partially corrupt. So after running a deep drive scan and thoroughly checking my registry out with absolutely no errors, I just started downloading it again and again. The 6th download worked. :-/

I find it so hard to believe that when downloading a fairly large file that that 5 times in a row, from various sources on the net, that it would come down corrupted each time. Never seen anything like it...