how much do you help you kid with a science project? I hate science projects! My son has to make one of those big boards and go all out on it. Its the first year he does one so major.
let your son come up with is own ideas, take him to the craft store or help him look up online what you'll need to buy and then have him draw a blueprint thing before he does the official project on the board. making several examples is really the best because he'll see the project in different ways.
get him to gather up all the info and explain to you how he see's it looking. you'll have to help him with some assembling and teachers expect that. as far as the necessary info/facts/data he'll need to provide, help him weed through the facts so he can keep it simple and concise.
my daughter is in 8th now and still comes to me with advice on projects, but she was always very independent about her work.