Hi guys, hope you can help me

I have an app that I need to add some sort of password control to.
Basically what I want to happen is when someone tries to switch from the app to another window(Excel, Word, etc) I want to load another form which will request a password, and if the password
is correct will then give control over to the other app, otherwise
it will 'disable' switching to the other app by keeping my app in
focus.

Any ideas

Thanks
John Neary