About the Afghan tax that was mentioned earlier--I heard back from my friend and this is what he had to say about it..
"I have not heard of any such tax. I even asked a few of the guys and they are unaware of it. However in order to avoid federal income tax an individual must be outside the US for no less than 330 days. At that point a tax credit will be paid to that person. The 20% may come into play is if the company that an individual is working for does not take out any taxes at all (Pays them as a contractor w/1099). And that person does not stay out of the US for at least 330 days. The tax obligation would be roughly 20-25% of the gross pay."