I am likely to get a rank between 400 and 500 in iit-jee 2011. What is best for me: Aerospace @iitb OR cse/microelectronics @iitm?

Well it totally depends on your field of interest and what you think would be perfect for your career as both Aerospace and CS/microelectronics are well suited fields for a individual, so I would suggest you to please concentrate on what field you thinkwould be as per your interest and will as also as per the rank you mentioned here you think you would get is no doubt outstanding which I can assume you might have even studied a lot.