Well if you bought those songs on iTunes I think it’s easy to get them back, because they should be linked to your account so you can download them for free again.
But if those music on your ipod are from other computers via itunes, you may not transfer them from ipod to pc because itunes can only transfer these fiels from itunes to your ipod touch. In that case you will need some other tools to do that. Google iPod Transfer
and maybe you can find something useful.