I would expect this effort to be loaded with issues. EPIC 5.1 is very old and was not certified to run on modern computers. You might get lucky and be successful using it for authoring as a 32-bit program but if you are only authoring, just install a modern version of Arbortext Editor. I'm sure they tried to make the underlying code platform independent but I would not guarantee that was truly successful.
I haven't tried Epic 5.1 on Windows 7 x64 but you should be able to get it working. If not, Windows 7 comes with Windows Virtual PC and a license of Windows XP. This mean you could run Epic inside the Windows XP mode of Windows 7.