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

uses IdMultipartFormData;

 { .... }

 procedure TForm1.Button1Click(Sender: TObject);
 var
   data: TIdMultiPartFormDataStream;
 begin
   data := TIdMultiPartFormDataStream.Create;
   try
     { add the used parameters for the script }
     data.AddFormField('param1', 'value1');
     data.AddFormField('param2', 'value2');
     data.AddFormField('param3', 'value3');

     { Call the Post method of TIdHTTP and read the result into TMemo }
     Memo1.Lines.Text := IdHTTP1.Post('http://localhost/script.php', data);
   finally
     data.Free;
   end;
 end;