You will be taxed as if you were a Citizen (Resident Alien) filing Form 1040 if you are a permanent resident (Green Card Holder) or you were present in the United States for 183 days for the three year period counting all the days in 2011, 1/3 of the days in 2010 and 1/6 the days in 2009.
As distinguished from Resident Aliens who are taxed on their worldwide income, Non-Resident Aliens are taxed only on their U.S. Source Income (by filing Form 1040NR). Many itemized deductions are allowed, though the Standard Deduction of $5,800 is not allowed.
Non-Citizens should reference the specific Tax Treaties with their respective Countries, which will further delineate rules on residency, deductions and the tax treatment of income.