I have the same problem. I remember one could remove a number of files and the oem install could be used on an existing o/s. I removed the hidden system files, no luck. Removed win.com too. I tried the /win98/setup /ntldr, that didn't work either, same message, basically says I have to purchase an upgrade.
Any new ideas picked up? I know it can be done, but it's been a long time. I don't want to loose the files on the drive.