There are a number of third party utilities that you can use to retrieve the files from your iPod. This is just a selection.
YamiPod Mac and Windows Versions
PodUtil Mac and Windows Versions
iPodCopy Mac and Windows Versions
PodPlayer Windows Only
PodPlus Windows Only
Have a look at the web pages and documentation for these and pick one you are happy with, they are generally quite straightforward.
There is also a manual method of accessing the iPod's hard drive posted in this thread:
MacMuse - iPod to iTunes
You may already be using the iPod in manual update mode in which case you can ignore the rest of this post. In manual mode, your iPod is safe from being accidentally erased. However if you are getting a message that your iPod is linked to a different library and asking if you want to link to this one and replace all your songs etc, click
*No*. Your iPod should appear in the iTunes source list. Change the update setting in Preferences>iPod to "manually manage songs and playlists"
Managing Your Songs Manually
You can also use a keyboard command to prevent your iPod auto-syncing with iTunes. While connecting the iPod to the computer on a Mac hold down the Option and Command (⌥ and ⌘) keys, on Windows, hold down Shift + Ctrl. This will stop the iPod from auto-syncing with iTunes and the iPod will appear in the source list. Wait until you are sure the iPod has mounted, and that it will not auto sync and then you can let the keys go. This may take between 3 and 30 seconds depending on your computer. Then go to Preferences>iPod and check the "Manually manage songs and playlists" box.
Keep your iPod in manual mode until you have reloaded your iTunes and you are happy with your playlists etc then it will be safe to return it auto-sync again.
Just to reiterate, the iTunes Warning.
If at any stage iTunes brings up a dialogue window asking whether you want to replace the songs on your iPod with the songs in iTunes, press "No". Pressing "Yes" will irredeemably remove all songs from your iPod.