I've registered a macro with Excel 2007 in order to look how to regulate the internal margins of a comment with a text inside.
The macro that I automatically obtain is: 

Sub Macro1() 
    Range("A1").Comment.Shape.Select True 
    Selection.ShapeRange.TextFrame.MarginLeft = 34.02 
    Selection.ShapeRange.TextFrame.MarginRight = 19.84 
    Selection.ShapeRange.TextFrame.MarginTop = 19.84 
    Selection.ShapeRange.TextFrame.MarginBottom = 19.84 
End Sub
but when I run this macro the only thing that I see is the comment shape selection; the internal margins of the text remain unaltered.
I've noticed two facts:
1) there is a check box "Automatic" inside the Margins dialog but no trace about its selection inside the macro.
2) if I insert in cell A1 a comment with internal margins previously altered the Macro1 brings again the comment text always in these positions (different from macro's values): 

.MarginLeft = 5.67 
.MarginRight = 9.92 
.MarginTop = 3.69 
.MarginBottom = 6.52
That's really very strange!
How is possible to solve this issue?
Thanks.