get the book. everything you need to know to pass the course is in the acls provider manual. and do not waste your money on any of the acls help texts on the market. i have not personally reviewed any of these manuals, so they may contain nice to know information, but all of the information required to pass acls comes from the acls provider manual.
if you want to read deeper than the material contained in the provider manual, the 2005 american heart association guidelines for cardiopulmonary resuscitation and emergency cardiovascular care
are all available online. if you opt to review this material, i would not do so until after
you have read and have a good understanding of the material in the provider manual.
don't let people scare you with horror stories of acls from the dark ages. it is no longer the nail biter that is used to be, nor are the instructors out to fail you. you do need to be familiar with the material.
relax, study the text, and you will do fine. good lucktime in a med surg text preparing for acls because you are probably not going to get what you need for!