Preventing a user from switching to another application is possible under Windows 3.x and 9x by tricking Windows into thinking a screen saver is running. This method does not work under Windows NT and is not guaranteed to be available in future versions of Windows. Many versions of Windows may also respond to a task switching trap installed by a CBT (Computer Based Training) application hook. To prevent task switching under Windows NT, you will need access to a third party keyboard device device driver.
VAR
OldValue: Longint;
[..]
// turns trap on:
SystemParametersInfo(97, True, OldValue, 0);
// turns trap off:
SystemParametersInfo(97, False, OldValue, 0);