Hi Simon,
Im only fairly new to astrophotography but I believe if you take Darks, Flats and Bias frames along with your main photos (light frames) you will be able to get rid of the dust specs, ISO noise and ... something else
hehe ... cant remember.
It took me a bit of reading to figure out what actually had to be done - youtube also helped alot - check the
DSS FAQ for some basic info.
If you have any questions id be happy to help - or at least try
Cheers.