I was referring to the image mounter portion of the application, which apparently requires the OS to be 32-bit in order to make the proper low-level hooks into the system. The rest of the WinISO app works as intended just fine on 64-bit Windows however.

If you are looking for a utility that mounts disc images, check out MagicDisc. It's freeware and works with both 32-bit and 64-bit versions of Windows (even as far back as Windows 98)

http://www.magiciso.com/tutorials/miso-magicdisc-overview.htm