don't. i also used to really think i needed a course to force myself to spend time, and was THIS close to doing so, but.. considering the prices of the SAT courses, it's not worth it. plus, they don't teach you anything you wouldn't have learned yourself if you had just spent the time to take practice tests and look over your answers.
you just need to take enough tests and KNOW what ETS is looking for, enough so you know the structure (not needing to read instructions and knowing how to manage your time), know that the english they test is standard english, and that many things that are appropriate in spoken english are wrong. practice using a watch. know when to cut your losses. know how to cross out answers, and to skip tiny tiny details in passages, and reread the question after you choose your answer, just to make sure one more time, and yeah. you can learn these things without a stupid course, just through practice alone. and potentially save hundreds or more... think about it, ~$50 in practice books cheap from half.com, or $300-$1000 in a course that's not even substantially more helpful.
on the other hand, if money is no object, then there are a few courses that i hear are okay. such as testmasters or ... eh. maybe testmasters is bad. i think there's something better than testmasters, but i'm short on time right now, so you can find that out yourself.
so.. yeah, i'd recommend not taking it, but it is always comforting to have someone with experience hold your hand all the way through. it's your choice.
fake edit: oh and btw, happy halloween!