제가 메인 폼에서 버튼을 클릭하면 폼을 show 하고 각각 모니터로 보내도록 했는데 맞는지 봐주세요..
제가 실행시켜보니까..에러가 나더라구요....

unit uMain;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;

type
  TfrmMonitorMain = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  frmMonitorMain: TfrmMonitorMain;

implementation

uses uOneMonitor1,uTwoMonitor2,uThreeMonitor3;
{$R *.dfm}


procedure TfrmMonitorMain.Button1Click(Sender: TObject);
var
   a : integer;
begin
   frmOneMonitor.Show;
   frmTwoMonitor.Show;
   frmThreeMonitor.Show;

   a := Screen.MonitorCount;

   frmOneMonitor.Left := Screen.Monitors[0].Left;
   frmOneMonitor.Top := Screen.Monitors[0].Top;

   frmTwoMonitor.Left := Screen.Monitors[1].Left;
   frmTwoMonitor.Top := Screen.Monitors[1].Top;

   frmThreeMonitor.Left := Screen.Monitors[2].Left;
   frmThreeMonitor.Top := Screen.Monitors[2].Top;

end;

end.