You need iPod to itunes Transfer to transfer your songs/videos to itunes,try Cucusoft iPod/iPhone to itunes Transfer,
it is a very handy tool for windows user to transfer music songs, playlists, video files and more from iTunes to Computer. Download at
GOOD LUCK!

ipod can only sync with one computer itunes. itune blocks this function since itune is the tool with one way to transfer files from itune to ipod. you must utilize other tools to achieve that. There’re couple of tools for transferring the files between ipod and computer (for backup)depends on your demands, e.g transfer only songs/videos, transfer photos etc. You can have a look of below review site, hope it useful.

1)open Itunes
2)open preferences on Itunes
3)open my computer
4)plug in Ipos
5)go to Ipod in my computer
6)copy music folder
7)paste somewhere else in your computer, not under Itunes
8)unplug Ipod, using safely remove hardware in lower right corner on toolbar
9)close my computer
10)close Itunes preferences
11)File>add folder to library
12)go to music folder from ipod, double click it
13)listen to music
it’s been a while, i’m 99% sure thats it.if there’s some subtlety i missed, go to apple.com, get to the answers part (that is similar to this one) and search for your question. after much searching, you will find it

try using the ipod as a hard drive (i think you can do this with tthe nano)..if you cant see it on the windows explorer windows ..go to folder options and have it reveal all hidden folders…..know that for a touch you cant do taht unless you have the touch jailbroken and have open ssh and winscp