I need to create a simple Delphi application, kiosk style.
It is a very simple thing, a single form where the user writes some personal info to register to an event.
I think you'd better create a new desktop, and run your app in there. When your app is done, you can bring back user's desktop. That is how Windows login screen works. Of course Windows login screen uses a special secure desktop. Your app in a separate desktop would be isolated. You will have a desktop background with no start menu, taskbar, or desktop icons because explorer.exe is not running there automatically. Of course a can start a new process, using Task Manager, but desktops in Windows are securable objects; therefore, you can make restrictions if you want. Of course if your app has sufficient permissions.
To create a new desktop, you can use CreateDesktop Windows API, and to switch to the newly created desktop, you can use OpenDesktop function.