Well, everything is okay now. Finally! To recap:
After the imaging of the hard drive, partition letters after the 'C'
(booting) partition became mixed up. This meant that programs trying to load
from 'E' could no longer find their .exe (or whatever) files and others
running from CD couldn't 'see' the CD drive because it was no longer 'D' (it
was moved to 'H', or something).
I phone the PC guy who said that changing the drive letters in THIS CASE
would be okay because everything was loaded with the previous drive letters
(all the registry entries still assumed that the CD drive was 'D', etc.).
So - with my heart in my mouth! - I changed each partition drive letter in
Disk Management (Admin. Tools). Now it's sweet as a nut!
(Remember that the important 'C' drive, which has Windows XP on it, was not
affected by this mix-up. The mix-up was not a fault, it was because on
restoring individual partition images, each partition was labelled
consecutively by default as 'C', 'D', 'E', etc. - but the 'D' should be
reserved for the CD/DVD drive on my wife's Dell.)
Anyway, just thought I'd let you all know it all panned-out. :-)