How can I create another itunes library on my computer?

I already have one library ... need another one for a different ipod ... also, the ipod that i need to create a library for already has songs on it ... the ipod was a friend's and i NEED to keep everything currently on the ipod - on the ipod, not erasing anything ... how do i do this and make sure that the songs on my new ipod are not erased when i sync it with a new library ... thanks in advance :)