As it turned out, that machine had a solid motherboard and a 10,000 RPM (! My wife needed a spare box to use as a scanning workstation and rather than run out and buy a new machine, I scoured the boneyard, finding this beast.
Finally, only use Windows XP to follow these steps; using a different version of Windows will break the install disk so that the installation won't recognise your CD key.
First, you'll need to download the Windows XP SP3 Network Installation Package, which is the standalone install for XP.
'There are no current plans to remove existing Windows XP security updates from Windows Update after end of support on April 8, 2014,' a spokesperson confirmed." .
The fact is, none of us will have looked everywhere and we will find some forgotten machines.
See Third Party Vendor-Specific Support Terms on Oracle Software Technical Support Policies (pdf) for details.