Andy’s Tech Experiments upgraded from MS-DOS to every subsequent version of Windows, along with Doom 2 and Monkey Island originally installed in DOS, to test compatibility:
The whole procedure took 3 days, of which approximately 12 hours was spent doing the actual installing – the rest of the time was spent trying to obtain valid copies of windows. One of the biggest problems was that Windows 95 and 98 came in two versions – Upgrade and Full. I had old disk copies of every Full version of Windows, but they cannot upgrade earlier versions. Luckily I was able to borrow a Windows 95 upgrade disk from a friend, and 98 was installed by renaming system files to trick it into upgrading.