This object contains the text in the text frame as well as the properties and methods that control the alignment and anchoring of the text frame. Use the TextFrame2 property to return a TextFrame2 object.
Set myDocument = Worksheets(1)
With myDocument.Shapes.AddShape(msoShapeRectangle, _
0, 0, 250, 140).TextFrame2
.TextRange.Text = "Here is some test text"
.MarginBottom = 10
.MarginLeft = 10
.MarginRight = 10
.MarginTop = 10