I no longer think it is a registry key issue. Using the Microsoft tool Stephen recommended with the second code Harm provided got me past the initial problem, but then the install failed later with an error trying to install some component.

I have provided DEA with an install log file and they are looking into it (I guess trying to work out if it is worth the effort for a no-longer-supported OS ).

I'm thinking of trying it on a clean (i.e. brand new) Win7 VM.