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Richard, While I have been unable to install AutoCAD R14 directly into a Windows 8.1 64-bit installation, I have been able to get it working. I simply copied the entire C: Program Files AutoCAD directory structure from an existing 32-bit XP installation to C: AutoCAD on the Windows 8.1 machine. I start it with a link to C: AutoCAD ACAD.exe.
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There were a couple of files (HEIDI3.DLL & GDIFONT3.HDI) that were flagged at startup and I had to move them from the XP C: Windows System32 directory to the 8.1 C: AutoCAD directory to get it to start and load a drawing. (You might be able to fix this equally well by reconfiguring AutoCAD's search paths.) Also, there is some problem with AutoCAD directly accessing a network drive at this point. But the system has even recognized and associated.dwg files with AutoCAD. I only installed Windows 8.1 yesterday so I was quite surprised by how well it seems to work: I am able to load, modify, save and print drawings with no apparent problems.