How to put songs in ipod?

I have an old model of ipod nano and formatted for windows. I have a mac on my office but i can't put any music or videos in it. I can updtae it but we don't have internet connection in here. if I do sync it, my entire library will be wiped out, and I have gazillions of songs! haow can transfer my itunes songs into my ipod without erasing my ipod..