My sister got a new laptop recently, and had about 600 songs on her iPod. Because her library was on that old laptop, the new one kept asking to sync and erase all the existing music on the iPod.
She didnt want to lose it all so asked me to back them up somehow.
After a bit of searching for software, I found a great little free app for doing this, called SharePod. Its for PC only but I think there's one for the Mac called SenUtil, but I havent tested that one. There's another one as well for Windows/linux/Mac called YamiPod but I havent tested that either, since SharePod did the job for me straight away.
Anyway, just in case anyone is stuck, one of those programs will work.