A screensaver is, in fact, an executable file that has had its file-extension changed from ".exe" to ".scr." If you don't change a screensaver's ".exe" extension, it will still work when you execute the file. However, if you add it to the System32 folder of your Windows directory, it won't appear in the "Display Properties" list. You must change the extension to .scr before Windows can add the screen saver to this list.
Use Windows Explorer to open the folder that contains the executable file that you want to convert into a screen-saver.
Locate the file you want to use, which will typically have an EXE file extension. Your .exe files may be hidden by default. If so, follow step 3 below. If not, skip to step 4.
Select Tools, Folder Options, and click on the View tab. Scroll down the Advanced Settings list and select Show hidden files and folders. Check Show hidden files and foloders. Click Apply to save the new setting. Click OK.
Select the .exe file you would like to convert and right-click on it. Choose the option to Rename in the drop-down menu.
Change the file extension from ".exe" to ".scr"
Right click the file again and then choose the option to Install.
Tips & Warnings
If you are creating your own screensaver, be sure to compile it at max scale and without frames. You should also ensure that it is always-on-top.
If you would like to use the screensaver as a slide-show, Microsoft DirectX may come in handy for creating transitions between multimedia.