I discovered what the problem is on Windows XP with SP2. I tried to install the following problems - Terragen, PowerBASIC 7, Dev C++ 4 and Typing Manager 2001. All these programs started to install then abruptly failed with no error message after creating temporary files beginning sc*.temp. Realising these may be 16 bit processes, I checked Autoexec.nt and Config.nt in the Windows/System32 directory. Config.nt contained the following lines:-
dos=high, umb
device=%SystemRoot%\system32\himem.sys
files=40
device=C:\PROGRA~1\ALWILS~1\Avast4\aswmonds.sys
Suspecting that it may be aswmonds.sys that was preventing the installs. I changed the line containing Avast 4's aswmonds.sys to:
REM device=C:\PROGRA~1\ALWILS~1\Avast4\aswmonds.sys
to test my theory. All the 16 bit programs mentioned above installed with no problems!