.
I found the answer by myself:
It works with the Windows API.
{
HWND hWnd;
HICON hIcon;
// -- get window handle of the panel
GetPanelAttribute (iPanel, ATTR_SYSTEM_WINDOW_HANDLE, (int *)&hWnd);
// -- load the icon file
hIcon = LoadImage (NULL, "test.ico", IMAGE_ICON, 16, 16, LR_LOADFROMFILE);
// -- if icon was loaded successful
if(hIcon)
{
// -- set the (small) icon !
SendMessage(hWnd, WM_SETICON, ICON_SMALL, (LPARAM)hIcon);
}
}