To bring it down to a pragmatic level - 2 possibilities (1) for purposes of the OEM license Microsoft considers a "PC" to be almost any piece of hardware internal to a CPU. This would seem to have possibilities- maintain one piece common to a "known licensed" machine and then it should work, provided the other PC is not currently using the license. (2) for a while anyway, if I recall correctly, MSFT policy was that a current product license would allow you to install previous versions in lieu of it on a licensed machine. If this is still true, you could aquire something along the lines of Windows 95 and install DOS 3.3 (as a prior product) instead of the Windows 95. You could not, of course, then install the 95 on another machine. MSFT was strangely quiet about *how* you would get the prior versions if you didn't have media, but as far as I can see the license is the important part.