You may do it in this way:
Code:
Dim MaxWidth As Integer

If Len(Your_Text)  > MaxWidth Then
     MaxWidth = Len(Your_Text)
End If

MSFlexGrid.ColWidth(Your_Column) = MaxWidth
MSFlexGrid.TextMatrix(Your_Row,Your_Col) = Your_Text
This is just an idea. You may have to modify it for working..