The RIAA has mandated that the transfer of music from the iPod to a computer, any computer, is not something that should happen. Go figure. This option is not available in the regular iTunes program.
However, there are a number of programs that will allow you to do it. Just Google for them.
If your iPod was used on a Mac then it is almost certainly formatted for that system. Reformatting to suite the Win world will destroy all your music.
Once again, there are pieces of software out there that will all the Mac formatted iPod to be read by a Win Machine.
BTW, the Mac can read both formatted versions.
Good luck in your quest