Weird, thanks for that link, Chris. There was a mass of Office 2007 stuff in the registry, a pile of old Visual Studio junk as well. Who would have guessed that Visual Studio was anything but a graphic image editor!
Anyway, rebooted and tried to install, continued to get the "Program too big to fit in memory" error, after about 30 attempts to get this running but closing the firewall, anti-virus, everything to get more memory, I'd given up for a while, had all the usual programs loaded, email, web browser with 4 open tabs, 2 newsreaders, Messenger, Apache web server ... inserted the CD - bingo!
Does too much free memory make the memory check go wrong?