Can’t install applications in Win 2000

Various SETUP.EXE install programs either won’t run or don’t complete properly in Windows 2000 Pro SP1. I am logged in as Administrator, there is masses of free disk space and memory, there is a valkid temp directory, proghram files directory, WINNTdirectory. I have run the protected files checker and checked everything else I can think of including the MS KB. It’s not just one install program – APCC’s Powerchute won’t run at all, IBM’s ViaVoice 8 runs but fails to install half the files, MS’sOffice 2000 runs fine with no problems, but Autoroute won’t run at all. Can anyone suggest ideas?