Thanks Geek-9pm that has a lot of information directly about my problem, and possibly a new answer to it.
Its interesting that my Dell actually accepted the Sata drive quite readily and saw it in the bios as WD 5000... so on then, because as I remember, I bought the Sata and therefore I must have had the disk at that time to install Windows XP as the operating system. I have been using it ever since and that now is over 2 years that I can think of.
I changed that all back to where it all works. (Maybe I'll take that challenge in the morning when I,er, wake up)
I went back to jason2074's reply and focused on doing the steps more carefully from
this link and suprise surprise it seems to have progressed to what I would call "A SUCCESS".
So far I have tried to download Adobe updates, that previously, would instantly fail (with a little code in the box) and installed a webcam from Logitech, to test the installer. Both have been successful, installing completely and appear operational.
I am thinking now that going through your link jason2074, with a bit more care (and a lot less alcohol)
has worked for my problem. Thank you once again for your researching it.
I'll have to test it over the next few days to confirm that it is resolved.
Thank you to everyone for their input. ImnoGuru