complex macro

Its not totally clear where you want to put your formula - an attachment would help.

Getting the months can be performed with this macro.

Sub AddMonths()
For N = 1 To 12
    Range("L65536").End(xlUp).Offset(1, 0) = Application.Text(N & "/1/07", "mmm")
Next N
End Sub

giving the name of the month in the language of the regional setting.