I was in a similar position when I started college. Back then, being a virgin was far less the norm than today. My experience with these things is honesty (or comfortably close to it) is the best policy. Just tell them you don't like casual sex and aren't looking for an intimate relationship right now. You'd be surprised how many people will admire you for being up front and real. Those who don't respect your choice and feelings aren't worth worrying about anyway.