i assumed that there is a "model" for the months sheet
http://www.cjoint.com/c/EHbeCbeGRma


Sub test()
oTab = "" & Year(Now) & "-" & Format(Month(Now), "00")
oExists = WorksheetExists(oTab)
If Not oExists Then
Sheets("model").Copy After:=Sheets(Sheets.Count)
ActiveSheet.Name = oTab
LastRow = 4
Else
LastRow = Sheets(oTab).Cells(Rows.Count, 3).End(xlUp).Row + 1
End If
Sheets(oTab).Range(Cells(LastRow, 3), Cells(LastRow, 6)).Value = Sheets("paste
two columns").Range("C2:F2").Value
End Sub

Public Function WorksheetExists(ByVal WorksheetName As String) As Boolean
On Error Resume Next
WorksheetExists = (Sheets(WorksheetName).Name < "")
Err.Clear
End Function

isabelle