Here's a step-by-step:

1. Copy code below:

Sub CommentDateTimeAdd()
Dim strDate As String
Dim cmt As Comment

strDate = "ddd, mm-dd-yy h:mm AM/PM"
Set cmt = ActiveCell.Comment

Set cmt = ActiveCell.AddComment
cmt.Text Text:=Format(Now, strDate) & Chr(10) _
& "NOTE:"

End Sub

2. Open a new workbook
3. Click on "View Code" from any sheet
4. On the Visual Basic window click "InsertModule"
5. Paste code into Module1
6. Return to sheet
7. Click "ToolsCustomize" and a window pops up
8. Select "Insert" menu at top of page (not in the open window)
9. Select "Comment" from drop-down menu from "Insert"
10 Right click and select "Assign Macro" from drop-down menu
11 Click on "CommentDateTimeAdd" from Macro window"OK", window closes
12 Click "Close" on the still open "Customize" window

Am I missing anythng?

K