I actually sat down and compared the 2004 Kaplan
with the 2003 Kaplan
at my local Barnes & Nobles a few weeks ago (they still had copies of the 2003 Kap even though they just stocked the 2004 version).
Although I basically skimmed both -- focusing in on parts of interest to me -- from what I can tell THEY ARE EXACTLY THE SAME BOOK! They may well have slightly different formatting but they are essentially the same book.
If you are interested in the CD-ROMs as well, they appear to be the same (the same version number). The only noticeable difference (without actually having tried the 2004 CD-ROM) is that the CD cover design is different.
So if you have the 2003 Kap, then save your money and don't buy the 2004 version. Someone else did mention that there might be some advertisement for some free services offered in the 2004 book. I'm not sure that it would be worth buying essentially the same book just for that. I think that if you went to the Kaplan
website, you probably could get the same deal without having to buy 2004 Kap.