iPod music to Mac

I have two computers with iTunes. All the music from Computer 1 has been downloaded to my iPod. I would like to download all that music onto Computer 2. However, Computer 2 has newer music on it that is not on my iPod/Computer 1. I can't figure out how to get the music from my iPod onto Computer 2 without erasing the new music. Suggestions? Thanks.

PS: Both of computers are on Mac OS.

The music on computer 2 won't be erased but the music on the iPod will be erased. If this music was purchased through iTunes and all through the same Apple ID then they can be downloaded onto the computer through the iTunes store. For non-protected music on computer 1 you can just make a back up copy cd then load that cd onto computer 2. For any protected music you would need to make certain it was purchased through the same Apple ID and that computer 2 is an authorized computer under that Apple ID.
Know more about "how to transfer or backup music from iPod to Mac", which included the detailed tutorials of how to transfer or backup your music from iPod to Mac.
Best wishes.

Tutorial Link:
http://www.softwarebbs.com/wiki/How_to_transfer_or_backup_music_from_iPod_to_Mac