Ipod, connect to more than one computer abd not have to erase songs every time?

i have a 2nd gen ipod nano 4 gig and i want to get songs off of a computer that is not mine. i know that there is a way becasue some ppl do it, but i dont know howw. i know how to add songs to the hard drive of the ipod, and then put them on the computers hard drive that you want to you. it just takes too long. anybody know how to so it where you acctually use itunes