To transfer music from your iPod to you computer follow these steps:
1. Connect your ipod to your computer via the USB cable that comes with your ipod.
iTunes will probably ask you if you would like to sync up your iPod, just click no.
2. Once it is connected, open My Computer and look for the iPod drive. A new letter should be in the folder, probably (F:)
3. Now open the iPod drive and click Tools > Folder options > View Tab > Show Hidden Files and Folders > Apply
4. Now you should have a new folder called ipod_control. Open that folder up and you should see the following:
Inside of the ipod_control folder you'll be able to find the Music folder. Copy each one of those folders (named something like: F00, F01 ...) onto your computer in a new folder.
5. Open itunes and insert the new folder you created on your computer into: Library > Music
6. Now it's time to sync your iPod to this new computer with out losing all of your music.