S -- I didn't notice your question until just a few minutes ago. Here's the "official" answer from Apple (I'm pretty sure you're using a Mac, but just in case here's the Windows procedure as well) :
How to keep iTunes from automatically updating your iPod
Even when set to update automatically, there is a way to tell iTunes not to update iPod when you connect it to your computer.
Steps are different if you're using Mac OS X or Microsoft Windows.
Mac OS X
To start off, do not plug in the iPod yet. That comes later. First you'll log into your computer as a different user:
If you already have another user account on your computer that you can use, skip to step 8. Otherwise, steps 2 to 7 will create one.
From the Apple menu, choose System Preferences.
From the View menu, choose Accounts for Mac OS X 10.3 or later. If you have 10.2.8 or earlier, choose Users.
In Mac OS X 10.3 or later, click the + button. If you have 10.2.8 or earlier, click New User.
Give the new user a name and short name.
Click the Password tab, and give the user a password.
Click OK, or quit System Preferences.
From the Apple menu, choose Log out username.
Click Log Out in the window that appears.
Click the name of the newly created user in the login window.
Enter the password.
Click Log In.
Now that you're logged in as another user, it's time to get back to iTunes and your iPod:
Open iTunes.
Connect your iPod to the computer. iTunes presents a message that the iPod is linked to another music library.
Click the iPod button in the lower right corner of the iTunes window.
Click the "Manually manage songs and playlists" button.
Click OK.
Click the Eject iPod button in the lower right corner of iTunes.
From the Apple menu, choose Log out username.
Click Log Out in the window that appears.
Click the name of your original user in the login window.
Enter your password.
Click Log In.
Open iTunes.
Now you can connect the iPod without iTunes automatically updating it. Optionally, you can delete the user you created by following these steps:
From the Apple menu, choose System Preferences.
From the View menu, choose Accounts for Mac OS X 10.3 or later. If you have 10.2.8 or earlier, choose Users.
Select the user from the list.
In Mac OS X 10.3 or later, click the - button. If you have 10.2.8 or earlier, click Delete User.
Follow the instructions in the message that appears.
Microsoft Windows
To start off, do not plug in the iPod yet. That comes later. First you'll log in as the Guest user:
Skip to step 7 if the Guest account on your computer is already on. If it's not, the next few steps will enable it.
From the Start menu, choose Control Panel.
Open User Accounts (one click or double-click depending on your settings). In the bottom right of the window is an icon with a suitcase labeled Guest under the heading or pick an account to change. Skip to step six if the text underneath Guest reads "Guest account is on."
Click Guest.
Click the Turn On the Guest Account button.
Click the X in the upper right corner to close the User Accounts window.
Choose Log Off from the Start menu.
Click Log Off. Do not click Switch User.
Click Guest at the login window.
Now that you're logged in as the Guest user, it's time to get back to iTunes and your iPod:
Open iTunes.
Connect your iPod to the computer. iTunes presents a message that the iPod is linked to another music library.
Click No.
Click the iPod button in the lower right corner of the iTunes window.
Click the "Manually manage songs and playlists" button.
Click OK.
Click the Eject iPod button in the lower right corner of iTunes.
Choose Log Off from the Start menu.
Click Log Off. Do not click Switch User.
Click the name of your original user in the login window.
Enter your password.
Press Return.
Open iTunes.
Connect the iPod.
Important: Having the guest account on allows anyone with physical access to your computer to use your computer.
Optional: To turn off the Guest account:
From the Start menu, choose Control Panel.
Click (or double-click) User Accounts.
Click Guest.
Click the Turn Off the Guest Account button.
Click the X in the upper right corner to close the User Accounts window.
docs.info.apple.com/article.html?artnum=93779