>Were's my problem: I want that when my application/form is running user can't do anything such as running other applications, hit the start button...

You can do something like:

_screen.AlwaysOnTop = .T.
_vfp.Width = SYSMETRIC(1) + 5
_vfp.Height = SYSMETRIC(2) + 5

Which will hide all other applications and the task bar. Though, you can still get to the start menu with the keyboard. I'm not sure if its possible to get around that in VFP.