在 delphi中使用 ARP

Question

我的一段程序：
unit Unit1;interfaceuses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls,winsock;type
  TForm1 = class(TForm)
    Edit1: TEdit;
    Button1: TButton;
    Label1: TLabel;
    Label2: TLabel;
    Label3: TLabel;
    Label4: TLabel;
    Edit2: TEdit;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;var
MacAddr:dword;
PhyAddrLen: DWORD;
ret,srcip,destip:dword;  Form1: TForm1; function SendARP(DestIP: DWORD; SrcIP: DWORD; pMacAddr: PDWORD;
   PhyAddrLen: PDWORD): DWORD; stdcall;external 'IPHlpAPI.DLL';
implementation{$R *.dfm}procedure TForm1.Button1Click(Sender: TObject);
begin
destip:=inet_addr(pchar(trim(edit1.Text)));
srcip:=inet_addr(pchar(trim(edit2.Text)));
ret:=SendARP(destip,srcip,@MacAddr,@phyAddrLen);
label3.Caption :=inttostr(MacAddr);
end;end.在调用SendARP时总是失败。那为DX给看看？谢谢
环境是win 2000+delphi 6