Luk505:
Download IRS Pub 519 from 
www.irs.gov (don't worry about the fact that it is for 2004; the IRS does not update all of their IRS Publications if the law does not change) and read pages 6 - 8.
Based on your input, it looks like you are 
not an exempt individual.  If so, you need to file Form 1040/1040A/1040EZ since you have more than met the Substantial Presence Test.