http://www.irs.gov/businesses/small/international/article/0,,id=96431,00.html
http://www.irs.gov/businesses/small/international/article/0,,id=96477,00.html
(You may be eligible to except a portion of your earnings if your home country has an established tax treaty with the U.S.) http://www.irs.gov/businesses/small/international/article/0,,id=96454,00.html