Ok. I've now started a post mortem to find out why I've got Oracle XE 10.2.0 / DOA / Delphi 7 working fine on one machine, and has been fine for 6 months, and on the other hand current Oracle XE, DOA downloads not working on both Win2K and XP.
I shall look for the differences and see if I can find out where the weakest link lies.