I want my screensaver appears in the screensaver preview box?
When you make a screen saver you need to support a command line argument (/p [HWND]) that will tell you in which windows to show your screen saver. The command line will be pass to you thru the screen saver control panel. here is a link to the full spec.
You can start the screen saver, get it's window handle then change it's parent to your forms handle or panel's handle or wherever you want it.
来源：https://stackoverflow.com/questions/903180/how-to-make-a-screen-saver-preview-in-delphi