>Is it possible for a form to cover the entiry screen (full screen) even the taskbar

It must be possible, because a lot of setup programs do it. I'm not sure what calls you'd have to make to do this, though.

> and not allowing it to minimize with ALT+TAB or windows key

You could set the MinButton property to .f., then call the Win32 API SetWindowPos() function with HWND_TOPMOST.

However, I hesitate to recommend even attempting this. This breaks a lot of UI standards, and could lead to frustration for the end users. If you're trying to control which applications a user can run, take a look at the Zero Administration Kit. If you're but one application on a system which has applications from a mixture of vendors, including yourself, I'd would advise against this approach if you're not the one responsible for administering these systems.