//本地時間
DateTime localTime = new DateTime(2011, 03, 10, 17, 32, 00);
//時區:美國
string easternZoneId = "Pacific Standard Time";
TimeZoneInfo easternZone = TimeZoneInfo.FindSystemTimeZoneById(easternZoneId);
this.textBox1.Text = TimeZoneInfo.ConvertTimeToUtc(localTime, easternZone).ToString();