Blimey. Absolutely nothing suggested in this thread so far has worked.
I cant even boot from a 3.5 to run the 3.9 boing bag installer over the 3.9 partition since the installer thinks I am attempting to install over 3.5 ;-)
Somehow, my configutation simply does not get on with OS3.9.
This is becoming a real nusiance. I never expected OS3.9 to be such an a*se.
Random things left to try
1) install under UAE and archive installation to a CD for extraction to DH2:
2) 'swapping' partitions to make the 3.9 install on 'DH0:' in case that makes a difference (no idea why it should)
3) Removing one of the 128M SIMMs in case for some odd reason that makes a difference (no idea why it should).
This is fast becoming a farce...