I think you're absolutely right when you say something is unstable with the hard drive, 'cos a file system could not be created due to a bad block. Had a look at the CMOS again and lo and behold it now only shows 33GB.
I'll probably go and buy myself a new hard drive and do as you say - keep this one for learning and experimenting.
Thanks for the assistance. One good thing to come out of this is - don't be scared of Linux - just get stuck in there and enjoy!