Getting week of the month from a Date

Getting week of the month from a DateTime variable
// ---- GetWeekOfMonth ---------------------------
//
// Assuming Sunday starts a new week, get the ordinal
// week a date is in...of the date's month
// using Microsoft.VisualBasic;

int GetWeekOfMonth(DateTime Date)
{
long Week;

// get first day of month
DateTime BaseDate = new DateTime(Date.Year, Date.Month, 1);

// get difference, in weeks, between the date and first day of month
Week = DateAndTime.DateDiff(DateInterval.WeekOfYear,
BaseDate,
Date,
Microsoft.VisualBasic.FirstDayOfWeek.Sunday,
FirstWeekOfYear.Jan1);

// want it one, not zero based
return (int)Week + 1;
}

// test it
protected void Button1_Click(object sender, EventArgs e)
{
DateTime Date = new DateTime(2007, 3, 1);

while (Date.Month == 3)
{
int Week = GetWeekOfMonth(Date);

Response.Write(String.Format("{0:d} : {1}
", Date, Week));
Date = Date.AddDays(1);
}
}