I m planning for a masters in US?

I m an computer engineering student and I m looking forward to do masters[m.tech] in US.I have already applied for immigrant visa and is expecting a call in around November..Do i need to give any exams like GRE or TOEFL?currently i m in my third year and so when do u think should i give my GRE if in a case i have to...and how much time does one need for its preparation.?which are the Financial aids provided that i should be looking out for?