主题：请问如何确定两个日期之间有几个星期一？

没有的，只能自己写代码：

Dim dt1 As Date = #1/1/2012#
Dim dt2 As Date = #5/20/2012#
Dim dt As Date
Dim cnt As Integer
For i As Integer = 0 To (dt2-dt1).TotalDays
    dt = dt1.AddDays(i)
    If dt.DayOfWeek = 1 Then
        cnt = cnt + 1
    End If
Next
output.show(cnt)