Thanks Mr. Knife,
I now have things working by calling the DOS program like
c:\blah\blah\prgm.exe <parameters>
This NOW works even though prgm.exe calls another DOS program in the same folder, etc. It didn't work earlier, but I think I had a typo in AUTOEXEC.NT. It now contains SET PATH=c:\blah\blah without %PATH%
That change in PATH does not persist beyond the program execution as far as I can see. Perhaps the "two PATH" situation had/has me confused.
I didn't use AUTOEXEC.BAT, given to understand that the "NT" extension was what was needed.
I'll follow your suggestions regarding the registry, etc., for a general solution.
Thanks again.
Proon comes through again.