Hello, I'd like to share my experience.
When I changed my computer, I used MediaWidget to move all library files from my iPod Touch onto my new computer http://www.gutensoft.com/Utilities/MediaWidget.htm
It can transfer all iPod content to the iTunes on your computer, including iPod music, movies, playlists, videos, podcasts, ratings, last played, and more. It's such a powerful one that many friends around me have used it for a long time. Easy and safe.
Now all files are on your new computer and iTunes, you can sync your iPod with it smoothly without deleting any files.
Just free download it to try.
For more iPod support information you can also go to http://www.apple.com/support/