Success!
Thanks for the feedback people.
Sorry I didn't reply sooner, my access to that computer was very limited, it was only today I got to try everything out. What we were trying to do was a complete wipe of the hard-drive, and install linux as the single OS for this desktop machine. No other partitions.

I'd already asked the woman there to try the 'fdisk' thing on the Ubuntu live version, but that didn't work. Seems bash didn't recognise the command, maybe she did it wrong, I wasn't there at the time to oversee.

Today I tried the Mandriva 2005 LE DVD, but that failed to install at exactly the same point. It failed to format the Ext6 Home partition on the drive. It just stopped responding at that point. So I went back even further and tried the Mandrake 10.1 Community release... worked like a charm! :D

Installed flawlessly, and after a few funny moments where it totally misconfigured the monitor, I managed to get it running smoothly. (It had set a 800x600 monitor as a 1024x768, resulting in some very odd graphical effects, and the mouse rolling over the right side of the screen and appearing on the left!!!). They might tentatively upgrade to the 2005 or 2006 LE later. If so, I'll let you know how it goes.

Great outcome. This computer had been a nightmare for ages, and the speed and simplicity with which Mandrake got the net and printers set up and running really dazzled the people I was setting it up for. They were really impressed; they seem keen now, eager to try it out... I think we have converts!

Let us continue to spread the good word!!!

Brad