Hi Meenakshi!
You are looking at about 8 months for the 4 sections. You may finish faster faster or slower depending upon various factors, mainly how much of a priority you can make it. You can take the 4 sections in any pattern you like, but you do need to finish all 4 in a 18 month window. There are changes coming to the exam in 2011, so you would be better off taking certain sections first in 2010.
You do not need to go to a class or join an institute, both Becker as well as Yaeger Review Courses have the self study package options, wherein you can listen to the lectures at home, after which you do the homework etc. Also, since your degree is from India, you need to send your transcripts to an evaluation agency, so that they make the determination that you are eligible to take the exam.
Hope this helps!
Anagha
AUD 94, BEC 88, FAR 85, REG 89