VBA if cell changed

Hi folks,
I'm a newb at VBA (and help forums), but I suppose everyone was at one time. I'm asking for your expertise with the following problem (Excel 2003)...

If the value of any cell in in column D is changed to "Closed", a message box will appear that says "Others must be notified when item is closed".
In that message box, I want two buttons:
Button 1 One is cancel and will undo the change.
Button 2 will open MS Outlook with pre-filled email addresses and will attach the open worksheet. After the email is sent, to return to Excel.

I have spent hours and hours trying to find the answer, I appreciate any help. Thanks a bunch.

SKP1