Connect your iPod to your computer. When you get the message that it is linked to a different library and asking if you want to link to this one and replace all your songs etc, press
"Cancel". Pressing "Erase and Sync" will irretrievably remove all the songs from your iPod. Your iPod should appear in the iTunes source list from where you can change the update setting to manual and use your iPod without the risk of accidentally erasing it. Also when using most of the utilities listed below your iPod needs to be enabled for disc use, changing to manual update will do this by default. Check the "manually manage music and videos" box in Summary then press the Apply button:
Managing content manually on iPod
Once you are safely connected there are a few things you can do to restore your iTunes from the iPod. If you have any iTMS purchases the transfer of purchased content from the iPod to authorised computers was introduced with iTunes 7. A paragraph on it has been added to this article:
Transfer iTunes Store purchases using iPod
The transfer of non iTMS content such as songs imported from CD is designed by default to be one way from iTunes to iPod. However there is a manual method of accessing the iPod's hard drive and copying songs back to iTunes on Windows. The procedure is a bit involved and was written long before iTunes 7 and Windows Vista so it requires a little adaptation as the iPod preferences are no longer in the location described for instance but if you're interested it's posted in this thread:
MacMuse - iPod to iTunes
If you prefer something more automated then there are a number of third party utilities that you can use to retrieve the music files and playlists from your iPod. This is just a selection, you'll find that they have varying degrees of functionality and some will transfer movies, videos, photos, podcasts and games as well. Have a look at the web pages and documentation, they are generally quite straightforward. You can also read reviews of some of them here:
Wired News - Rescue Your Stranded Tunes
YamiPod Mac and Windows Versions
iGadget Windows Only
Music Rescue Mac & Windows
iPodCopy Mac and Windows Versions
TuneJack Windows Only
iPod2PC Windows Only
Whichever of these retrieval methods you choose, 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. I would also advise that you get yourself an external hard drive and back your stuff up in case you have problems again. Relying on an iPod as your sole backup is not a good idea and external drives are comparatively inexpensive these days you can get loads of storage for a reasonable outlay.
