I'm aware of "screen tips" associated with icons on toolbars, but not
with cells. A similar thing for a cell is a "comment".

The following VBA code worked for me, although the sizing not very
well.

'add comment to cell
Range("C9").Comment.Text Text:="insert text"
'change size of comment
Range("C9").Comment.Shape.ScaleWidth 0.9, msoFalse,
msoScaleFromTopLeft
Range("C9").Comment.Shape.ScaleHeight 1.1, msoFalse,
msoScaleFromTopLeft
'copy comment from one cell to another
Range("C12").Comment.Text Text:=Range("C9").Comment.Text
'clear a cell's comment
Range("C10").ClearComments

Hth,
Merjet