Here's how to get the first full Moday to Sunday of the previous week...
Code:
        Dim MyDate As Date = Date.Now
        For J As Integer = 7 To 1 Step -1
            Dim OldDate As Date = MyDate.Subtract(New TimeSpan(J + MyDate.DayOfWeek - 1, 0, 0, 0))
            MessageBox.Show(OldDate.ToShortDateString)
        Next