I lived and worked in Manchester for a number of years. I walked to/from work, but still had a car for shopping and visiting friends and family. Groceries might be difficult without one but probably not impossible. But in NH, there are few or no options for public transit so unless you plan to never leave a 5 or 10 mile radius around your home, you'll need a car at some point. If you're in Manchester, I guess you could easily rent a car at the airport when you need it?