Автор: http://www.swissdelphicenter.ch

{ 
 I did not found property to know the rownumber of a TDBGrid, 
 so I will try this in the OnDrawColumnCell of a DBGrid: 
}

 procedure TformX.DBGridXDrawColumnCell(Sender: TObject; const
   Rect: TRect; DataCol: Integer; Column: TColumn; State: TGridDrawState);
 var
   RowNo : Integer;
 begin
   RowNo := Rect.Bottom div TStringGrid(DBGridX).DefaultRowHeight
   //so, RowNo has the Row to be draw in the moment 
  ...
 end;