I’ve finally, for sure this time, fixed the 64-bit installation issue. I confirmed that I tested 1.3.119 on a 64-bit machine, but perhaps there was an uninstall that didn’t remove all the necessary Registry entries, so I didn’t detect that the 1.3.119 installer didn’t create everything. I’m not sure. Anyway, I tested 1.5.122 on a clean Registry (64-bit) and it works. I apologize for any issues you’ve had.
Please let me know if there’s still an issue on your machine. If nothing else, I can give you a Registry file to import that will fix it.
I’ve re-designed the Web site to make it easier to use (good for you) and easier to manage (good for me). If something doesn’t work as expected, 
If you subscribe to the 12noon mailing list, you will receive one final e-mail at that address notifying you of the change. You can sign up for updates on the new 12noon.com home page.
Display Changer 4.3.2 has been released. I don’t know how this went unnoticed for so long, but the -top and -bottom switches should actually have been documented as -above and -below. I’ve corrected the documentation and updated DC so that all four of those switches work.