dragdrop with daatgridview

i have a form with a datagridview. i have implemented the functionality to be able to drag and drop the contents of a cell into another control. the only problem is i don't want the user to be able to drag and drop the header cells. i can't get the CellMouseDown function to differenciate between a header cell and a normal cell. i have tried using the row index properties but for some reason however coded the datagridview decided to give the header the same row index as the first row of data. the ability to sort the data by clicking on a header cell has also been removed as it just tries to drag the data. can anyone help me?