I'm applying for an internship to a big-name company and have an interview next week. This would be a great place to work, but it's not my first option. I want to work for another company that would better prepare me for that part of the industry, and that company doesn't start considerations until March.

How do I tell the first company that I need 6+ months to decide, without compromising my position there?

Edit: I'm a junior in college and this would be my last internship before I graduate.