hi i am a non resident alien of the u.s but i have a SSN. i want to open an onlne account ? i intend to report to the ir a 1040NR at the end of the year. do i have to fill a w-8 if i still intend to fill in a 1040 NR? if i fill w-8 will the broker withhold 30% on capital gains ( selling stocks?) what should i do ?