When iTunes introduced its version 7, they included a feature that makes it much simpler to transfer music from your iPod to a new (or different) computer. While it was possible before, it was a hassle to find a way to copy the music from your iPod to the computer. With the new backup feature it's a breeze to recreate your iTunes library.
Enable Disk Use
Confirm that your iPod is configured to enable disk use. Essentially this means that your new computer will recognize your iPod as a USB device device or a external drive.
Enable disk use if necessary. Connect your iPod to your old computer and open iTunes. When iTunes has loaded, select your iPod and display "Preferences" in the main window.
Click on the "Summary" tab and select "Manually Manage Music." You should see a check mark in the box next to "Enable Disk Use." If you don't see it, then just check that box yourself. An alert will display informing you'll now need to manually unmount the iPod as well as ejecting it in iTunes before disconnecting it from the computer.
Hit "OK" and click "Apply Preferences."
Move all your music to one place to make the transfer easier.
Navigate to the iTunes Preferences menu. In Windows, this menu is located in the Edit menu, while on a MAC it's simply it's own menu.
Go to the "Advanced" tab, then "General." Check the box next to "Copy Files to iTunes Music Folder When Adding to Library" and click "OK." iTunes will copy all of your music to the hard drive of your computer. This shouldn't be a problem unless you don't have enough disk space.
Go to the "Advanced" tab and then "Consolidate Library." Read the message that warns you that this step will place all your music in the iTunes folder and that it can't be reversed. Click "Consolidate."
Determine Storage Capacity
Make sure there's enough space on your iPod to hold the iTunes music files. In essence, you will be using your iPod as an external storage drive to bring your iTunes library to the new computer. Without a large enough storage capacity, this can't be completed.
Determine how much space is available by opening iTunes on your old computer
and checking the size of the library. Click on "Music" and make note of the amount of space your library takes up. Then connect your iPod, click on it in iTunes and note the amount of free space indicated at the bottom of the pane.
Calculate to make sure that the amount of available space on your iPod is greater than the space required by the iTunes library. If not, you'll need to free up some space.
Free up space by clicking on your iPod in the Source pane and then clicking on "Music" or otherwise navigating to the contents of your iPod. Click on any song in the main library window and go to "Edit, then "Select All."
Be prepared to lose any music not contained by your iTunes library if you haven't been updating automatically, because that music isn't on your computer and will be deleted. However, if you've been updating, there's no need to worry. Press your keyboard's "Delete" button and click "Yes" when you receive the confirmation message.
Copy and Backup
Exit from iTunes and locate both your iPod and your iTunes folder. On a Mac, the iPod should be visible on the desktop and the folder is "/Users/username/Music." In Windows, the iPod is located in "My Computer" and the folder is "\Documents and Settings\username\My Documents\My Music." Drag the folder to the iPod and wait patiently as the data transfers.
Copy your iTunes folder to your iPod. Drag the folder to the iPod and wait patiently as the data transfers. When it's done, eject the iPod from iTunes and disconnect the iPod.
. Connect your iPod to your new computer and backup any music that's in your new iTunes library. Go to "Preferences," "Advanced" then "Reset." Click "OK." Then navigate to "Advanced," "Consolidate Library" and click "Consolidate."
Copy your music to your new computer. Locate the Music folder on your new computer--it will have the same name as on the old computer--and drag the iTunes folder from it to the desktop. Find your iPod, double-click to open it and drag the iTunes folder copied from your old computer to the new computer's iTunes folder.
Wait as the music is copied to the folder and then open iTunes. The music and all of its accompanying information should sync without problem.