Take a look at the below article:
http://www.manhattangmat.com/blog/index ... an-part-1/(There are two parts to that article - at the end of the first part, follow the link to the second part.)
That article will help you to decide how you want to study, what materials you want to use, and so on. It also tells you how to get started (you'll take a practice test to see what your strengths and weaknesses are and then start from there).
You mention feeling very rusty with math. Depending on how you do on your first practice test, you may decide that you want more foundational / fundamental help with the math. For example, we have 5 "regular" math books that cover all of the topics tested on the GMAT, but those books do assume that you remember some of what you learned in school. We also have a Foundations of Math book for people who feel that they need to start from a more fundamental or basic level before they move on to the "regular" level.
Take a look and let me know if you have any other questions!