Автор: http://www.swissdelphicenter.ch

{
  This example shows how to fill out fields in your webbrowser by
  dragging the content of Label1 to a field of your webbrowser
}

procedure TForm1.FormCreate(Sender: TObject);
begin
  label1.DragMode := dmAutomatic;
end;

procedure TForm1.WebBrowserDragOver(Sender, Source: TObject; X,
  Y: Integer; State: TDragState; var Accept: Boolean);
var
  item: Variant;
begin
  //check if document is interactive
  if (Webbrowser.ReadyState and READYSTATE_INTERACTIVE) = 3 then
  begin
    item := WebBrowser.OleObject.Document.elementFromPoint(x, y);
    if Source is TLabel then
      Accept := True;
    Accept := (item.tagname = 'INPUT') and ((item.type = 'text') or
      (item.type = 'password')) or (item.tagname = 'TEXTAREA');
  end;
end;

procedure TForm1.WebBrowserDragDrop(Sender, Source: TObject; X,
  Y: Integer);
var
  item: Variant;
begin
  //check if document is interactive
  if (Webbrowser.ReadyState and READYSTATE_INTERACTIVE) = 3 then
  begin
    item := WebBrowser.OleObject.Document.elementFromPoint(x, y);
    item.Value := label1.Caption;
  end;
end;