I took my netbook along and let the young couple play
with it for an hour. That was enough to convince them. They are now
going to put Ubuntu on their PC!!!! In due course, when the dust has
settled, I'll install the second hard drive and re-format it for extra
storage.
Since installation, my sister's phoned me twice only for help. One was
because someone had sent her an MS publisher file. I told her her old
computer couldn't have read that either. She went to see the guy and
he's promised to send her PDF's next time, so no problem.
Next call - "Ubuntu wants to update me - is this safe?" In almost three
weeks, no problems at all and she's delighted with the speed her 'new'
computer runs at.