[C#]週番号の取得

VB6で言う所のDatePart(DateInterval.WeekOfYear, Now)をC#でやると。。。

Calendar cal = CultureInfo.CurrentCulture.Calendar;
CalendarWeekRule cwr = CultureInfo.CurrentCulture.DateTimeFormat.CalendarWeekRule;
DayOfWeek firstDay = DayOfWeek.Monday;

int weekNumber = cal.GetWeekOfYear(Target, cwr, firstDay);

こんな感じで取れました。
firstDayのあたりはお好みで。