The HDD is in the old computer.
I'm aware that this is taking up a lot of your time. Possibly one last try, and then I might look at the XP Pro solution I mentioned.
Yes, that worked fine, and I did a restart afterwards.
Yes, that all checks out, the file from the hotfix is 41 KB and dated 10/31/97. The computer boots up okay, and is in MS-DOS mode.
Ok, things are looking up.
I believe we have successfully removed the Demo RAM patch and XUSBSUPP. There should not be any more files left with .O20 extensions, and you should remove any remaining files we have used/altered such as VMM32.ERR, and leave only a backup copy of the 2005 VMM32.VXD, named VMM32.ORI. (Be sure to use that name, as XUSBSUPP uses the .O20 extension, and the RAM patch uses .BAK, so .ORI leaves us with an extension that will not be altered, deleted, or overwritten by any update.)
Does the computer still hang now that we have reached this step, or have we stopped that?
Now, as you encountered errors while the HDD was still in the "new" machine, and had to transplant it again, it is probably a good idea to go into Safe Mode and remove all of the devices from the Device Manager again to ensure that no devices detected on the "new" machine are still present. Then Reboot, and allow the machine to install drivers for the older hardware.
If you get any prompts about missing files, try manually directing the installer to C:\WINDOWS\OPTIONS\CABS or C:\WINDOWS\SYSTEM, if the required files are still not found, try other "logical" locations under C:\WINDOWS. If any are still not found, make note of what files they are and what device was requesting them if possible.
Hopefully this will correct the MS-DOS Mode issue and get you back to where you were.
Let me know the results. I must go soon for tonight though, as I have to work in the morning.