According to the Easons site only the 2001, 2002 or 2003 are currently available. See here [broken link removed] Site seems to time out on link so if you call the enquiry up under Author Bill Tyson you will get the necessary info.
It's hardly worth buying each year's update of books like this or Colm Rapple's Family Finance or the Taxation Advice Bureau's equivalent as all of the updated information is generally available for free from other sources. In fact you can read the TAB book (2004 edition) for free online:
Last December's budget was so bland that about 95% of the tax details etc in the 2003 book are still valid. Even if he had brought a 2004 version out it probably wouldn't have been worth your while buying it.
I would agree with daltonr on the Tyson book. I read last year's from cover to cover and thought it thoroughly excellent. It is a fair point though that I think you only need to buy these books once every couple of years once tax rates or policies have fundamentally changed.