With the rebuilding complete, it came time to investigate what to do with the Compaq. HP "helpfully" provided an eight page document describing how to disable Secure Boot. The effect of that document , perhaps intentionally, was to create the impression that disabling Secure Boot was tantamount to rocket science. I found the couple of relevant paragraphs and it turned out that to disable Secure Boot and EFI, and switch to Legacy Boot involved little more than entering BIOS and making a few configuration changes - all done in a matter of seconds.
I now have Mageia 3 installed on that machine. It is a small victory but I enjoy even small victories, when they are achieved over the Stalinists in Redmond.
Jim

Good to know that is does not take a triple somersault to disable secure boot in UEFI.