[ecfisa]

Hola patxim.

Proba de este modo:

Código Delphi [-]
type
  TDBGridEx = class(TDBGrid);

function GetFieldAtColRow(ACol, ARow: Integer; GR: TDBGrid): string;
var
  BM: TBookMark;
begin
  with TDBGridEx(GR) do
  begin
    if (ARow > 0)and( ACol > 0)and(ARow < RowCount)and(ACol < ColCount) then
    begin
      BM:= DataSource.DataSet.GetBookmark;
      DataSource.DataSet.DisableControls;
      DataSource.DataSet.MoveBy(1 - Row);
      DataSource.DataSet.MoveBy(ARow - 1);
      Result := DataSource.DataSet.Fields[ACol-1].AsString;
      DataSource.DataSet.GotoBookmark(BM);
      DataSource.DataSet.FreeBookmark(BM);
      DataSource.DataSet.EnableControls
    end
  end
end;

Llamada ejemplo:

Código Delphi [-]
procedure TForm1.Button1Click(Sender: TObject);
begin
  Caption:= GetFieldAtColRow(StrToInt(EditCol.Text), StrToInt(EditRow.Text), DBGrid1);
end;

Saludos.