Run an application with/as screensaver

Question

How do I add a custom application to run as a screensaver. Like calc.exe for example?

Answer 1

The solution was easy: rename Calc.exe to Calc.scr and it will appear in the Screen Saver Dialog box. But not all EXEs will work.

EDIT: Not all EXEs work in the C:\Windows\System32\ folder, but those that did not work there, work in the C:\Windows\ folder. These were the ones that depended on external DLLs. Something I noted, but I don't know how or why that is.