Multi-WIM seems to be installing ImDisk Virtual Disk Driver for Windows NT on the host computer.
I am using windows 8.1 x64 for the host computer. Don't see any box to check or uncheck to stop
this from happening. Any help would be appreciated.
Imdisk is used in MultiWim to create the boot image efisys.bin for the create ISO, if you choose the option "Add bootia32.efi... for dual boot 32/64 bit UEFI".
The installed version imdiskinst.exe is the latest stable v1.9.2 for Windows NT/2000/XP/Vista/7/8/8.1 or Windows Server 2003/2008/2012 and it Works on both 32-bit and 64-bit versions of Windows.
There is no worries with your windows 8.1 x64 system. Note also that It is installed only if it is not already installed.