You can manage your iPod with different computers as long as the computers are running the same operating system (Mac OS X or Windows) and you have set the iPod to "Manually manage music." If you're not using iTunes 7 or later, click here.
Using an iPod formatted for Macintosh on a Windows computer is not supported. Using an iPod formatted for Windows on a Macintosh computer is not supported. To determine your iPod's hard disk format see "iPod: How to determine iPod's hard disk format." To change the iPod format you will need to restore iPod using iTunes. For more information on the how to restore iPod with iTunes see "Restoring iPod to factory settings."
By default iPod is set to "Automatically sync songs to my iPod" sometimes called automatic mode. In order to transfer music from multiple computers iPod must be set to "Manually manage music" sometimes referred to as manual mode.
When iPod is set to automatic mode iTunes automatically updates iPod's music library whenever you connect iPod to your computer. iTunes transfers new songs you've added, and erases songs you've removed. However, the first computer you connect iPod to is its "home" computer, and the music library from that computer is copied to iPod. When you connect iPod to another computer, an alert box appears with this message:
"The iPod "iPod" is synced with another iTunes library. Do you want to erase this iPod and sync with this iTunes library?"
"An iPod can be synced with only one iTunes library at a time. Erasing and syncing replaces the contents of this iPod with the contents of this iTunes library."If you want to delete the music library on iPod and make the second computer iPod's "home" computer, click Erase and Sync. iTunes will delete all songs and playlists on the iPod, and then will copy the music library and playlists from the new home computer to iPod.
If you want to keep the music library on iPod, but copy songs or playlists from the music library on the second computer, click Cancel to this dialog box, and then set iPod to manual mode.
You change the iPod synchronization mode to manual mode in iTunes:
It is normal for iPod to take a few seconds to change from automatic mode to manual mode.
- Open iTunes, if necessary.
- Select iPod in the Source pane.
- Click the Summary tab.
- Click "Manually manage music and videos" to enable that option.
- Click OK in the resulting dialog box.
- Click Apply.
When in manual mode, to add songs or playlists drag them from iTunes to the iPod icon in the sidebar. To remove songs or playlists select them on the iPod in iTunes and hit the delete key. You can also create playlists directly on the iPod.
Information from http://docs.info.apple.com/article.html?artnum=61675