TStringGrid - Dragging and Dropping

I would like to determiine what row a drag and drop operation starts
and finishes on when using a TStringGrid.

I have a grid that has one fixed row and one fixed column and would
like to be able to 'Mousedown' on the fixed column and determine what
row I am on and then using what row I drop at, swap the two entries

Any ideas/solutions would be gratefully appreciated

Terry Benge