Hi,
I am an Indian student on F1 visa at Louisiana. I am getting full tuition waiver and graduate assistantship. I wanted to know whether as an international student I will have to pay taxes and if yes then how much tax will I have to pay. My asssitantship is 15,000$ annually. What will be the total amount of federal and state taxes, incurred on my income.
Please let me know ASAP.

Are you taking about 2007 return? Or it is for 2008 return?
The answer will depend upon what forms you will get 1098-T for tuition paid, 1042-S for scholarship etc. Even if you don't have taxable income, you must file Form 8843.