大尾巴狼

//就测试这天了
        DateTime testDate = DateTime.Now;

        //testDate = new DateTime(2005, 7, 22);

        //足够小的基准天（必须是星期一）
        DateTime baseDate = new DateTime(1989,7,3);

        TimeSpan ts = testDate - baseDate;

        int i = Convert.ToInt32(Math.Floor((ts.TotalDays) / 7));

       
        baseDate = baseDate.AddDays(i*7); //本周一
        baseDate = baseDate.AddDays(6); //本周末

   //DateTime TestDate = new DateTime(2005, 8, 28);
   DateTime TestDate = DateTime.Today;
   //选择合适的日历
   System.Globalization.Calendar calendar = new System.Globalization.GregorianCalendar();

   //把指定日期转换成所在星期(第几个星期)
   int Week = calendar.GetWeekOfYear(TestDate, System.Globalization.CalendarWeekRule.FirstDay, DayOfWeek.Monday);

   //因为要求星期一作为一星期的第一天,星期天作为星期的最后一天,所以要处理一下.
   int Days = (int)TestDate.DayOfWeek ;
   if(Days == 0)
    Days = 6;
   else
    Days -=2;

   //得到指定星期的起始终止日期
   DateTime FromDate = TestDate.AddDays(-Days);
   DateTime ToDate = FromDate.AddDays(6) ;
   
   Console.WriteLine(" 第{0}周 星期：{1}  起始日期：{2}  终止日期：{3}", Week, TestDate.DayOfWeek.ToString(), FromDate, ToDate);