How do you sync an iPod to a library on another computer without erasing the files?
Tansee iPod Transfer can help you . if you directly click sync, it will erase all music on your iPod and replace with the content of this new iTunes library.
But here is a solution. All you need is to get all existing music/videos from your iPod to this new computer and iTunes. Simply use this popular program called Tansee iPod Transfer
The whole process is easy and safe.
With just a few simple clicks, it will help you copy all videos/songs from iPod back to your selected folder on the new computer, and then you can easily add those songs back to iTunes.
More importantly, this won't overwrite any original files on your iPod. And all song names are preserved.
In this case, all songs/videos (both new and old) are on your iTunes library that you can syn with whenever you wish to without deleting any files.