Оформил: DeeCo
Автор: http://www.swissdelphicenter.ch

{ 
  The LockWorkStation function locks the workstation's display, 
  protecting it from unauthorized use. 
  This function has the same result as pressing Ctrl+Alt+Del and 
  clicking Lock Workstation. 
  To unlock the workstation, the user must log in. 

  Windows NT/2000/XP: Included in Windows 2000 and later. 
  Windows 95/98/Me: Unsupported. 
}


 procedure TForm1.Button1Click(Sender: TObject);
 begin
   LockWorkStation;
 end;

 { Loading LockWorkStation dynamically}

 function LockWS: Boolean;
 // by Thomas Stutz, SDC 
type
   TLockWorkStation = function: Boolean;
 var
   hUser32: HMODULE;
   LockWorkStation: TLockWorkStation;
 begin
   // Here we import the function from USER32.DLL 
  hUser32 := GetModuleHandle('USER32.DLL');
   if hUser32 <> 0 then
   begin
     @LockWorkStation := GetProcAddress(hUser32, 'LockWorkStation');
     if @LockWorkStation <> nil then
     begin
       LockWorkStation;
       Result := True;
     end;
   end;
 end;