Learn to Use your Computer

You may want to update your iPod automatically, but only with selected songs -- especially if your iTunes library is larger than the capacity of your iPod. To use this method, you must first select the songs you want to transfer to the iPod in the iTunes library and then deselect the songs you don't want to transfer.
You can quickly select or unselect an entire album by selecting an album in Browse view and holding down the Command key.
After selecting the songs to transfer, follow these steps:
Connect the iPod to your Mac through the Mac's FireWire connection.
Select the iPod name in the iTunes Source pane.
Click the iPod options button.
The iPod Preferences dialog box appears.
Select the Automatically Update All Songs and Playlists option and click OK for the "Are you sure you want to enable automatic updating?" message that appears.
Select the Only Update checked Songs check box and click OK.
iTunes automatically updates the iPod by erasing its contents and copying only the songs in the iTunes library that you selected.
Click the iPod eject button, which appears in the row of buttons in the bottom-right corner of the iTunes window (only while the iPod is connected).