Find out which sections your school tests on...mine did not test us on the science sections (Chem, AP, ect), you don't want to waste your time studying unnecessary info! I took the HESI in Nov 06 and had the study guide, which I did think was helpful.
For additional review, I went to www.testprepreview.com
(go the the Nursing Exam Practice link on the left). These quizes are intended for NET and TEAS review, but scroll down and there are all sorts of quizes for every area that the HESI tests on as well, Grammer, Vocab, Reading Comp, ect. Make sure you review your ratio and proportions and household measure, there were a lot of those type questions on the HESI I had! Honestly though, I thought the test was rather easy. I ended up with a 96% and that plus my 3.85 GPA has me starting nursing school
Don't stress, you'll do great!