You will need to use a program like TouchCopy to copy your iPod content onto your computer or straight to your new iTunes. TouchCopy lets you copy all your music, video, photos, contacts, notes, calendars, games and more from your iPod.
To copy your iPod music using TouchCopy, you will need to...
1. Download and install TouchCopy on your new computer. TouchCopy works with all iPod types and the iPhone. There are free PC and Mac downloads available from here
http://www.touchcopy.com
2. Ensure that iTunes is closed before connecting your iPod. Then start TouchCopy and connect your iPod. TouchCopy will have fixed your iTunes preferences so that iTunes will not sync music or video with your iPod while TouchCopy is running. These changes are restored when you quit TouchCopy.
3. Use TouchCopy to copy all your iPod content to your new computer hard drive or straight into iTunes.
4. You can then use iTunes to re-sync your iPod, which lets you add new content to it.