Keep in mind that networking at these events is not about being something you're not. It's about presenting yourself in a positive and professional manner. Move around as much as possible. Use the career fair as an opportunity to meet and network with people from companies you never would have met otherwise. Get in there and introduce yourself to the recruiters.
Employers use career fairs as a screening tool, too.
It is important that you present yourself as a serious candidate. Dress for success. You want to present a professional image. Don't wear jeans, sweats, ball caps or sneakers. Introduce yourself to representatives in a positive and confident manner.