Ativando e desativando o alt+tab

Desativa o ALT+TAB

procedure TurnSysKeysOff;
var OldVal : LongInt;
begin
SystemParametersInfo (97, Word (True), @OldVal, 0)
end;

Ativa o Alt+Tab

procedure TurnSysKeysOn;
var OldVal : LongInt;
begin
SystemParametersInfo (97, Word (False), @OldVal, 0)
end;