At one time, Polaroid offered a free dust and scratch removal tool. It is still available through the wayback machine. YMMV, but I have found with certain types of images (speckled and stippled type) it works wonders. Obviously, its usefulness will vary based upon your image properties but its another toolkit in your bag. It appears to work on all versions of Windows.
Link here:
http://web.archive.org/web/200710150...sr/pdsr1_0.exe