Sara,
I have heard people trash on the ARCO book, but I personally thought it helped prepare you for the test (all except for the BIO portion that is ). Granted, I didn't exactly "study" or prepare very well for the ASTB. The first time I saw the ARCO book was 15 minutes before the test, another NROTC Midn had one. I borrowed it for those 15 minutes, and looked over the spacial apperception parts, I think that, if anything, that was what truely helped me out the most. Thankfully I did NOT have to retake the test, I scored well on my first shot. But looking back, I think spending time going over the two flight aptitude test books out on the market would be worth the time and $$.
I looked over the other gouge packet floating around out there, and the math/mech info looks right on. If you don't already have it, it would be worth your time to reread some of the posts about it, and email the people that have it, I am sure they would gladly send it to you. It is more a matter of getting used to the types of questions that are going to be thrown at you, than anything else.
In the end, the ASTB is only the first hurdle of many, and for some it is a rough one to overcome (sorry Dave). Best of luck on it, I am sure some of the others on the forum have a "fresher" view on it, I took it close to 3 years ago, and it is pretty much a distant memory!
Brian, congrats on passing the ASTB, and best of luck with your package, glad to hear that the forum has helped you out.
Anyways, hope that info helps out some, welcome to the forum.