W2K Upgrade Install Error

I am trying to install Windows 2000 Upgrade (w SP1) into a PC with NT4 & Svc Pk 6a. Within the first minute and before actually starting anything, I get an error message stating the installer “..cannot determine the version of Windows..” and exits immediately. I’ve tried this in VGA mode, Off Line with same results. I need the info quickly. Any ideas or cures?