iPod sync with iTunes - new computer

I am trying to help a friend save her music that is on her iPod, and put it in her iTunes on her windows PC.  This is a new laptop, as here old hard drive gave out.  For some reason, the iTunes on her new computer won't let her download the iPod music, and it wants to wipe out the iPod.  I don't quite understand what Apple is doing here and why she can't sync her music.  I am sure they look at it as some sort of license violation.  However, my friends has converted most all of her old CD collection to the iPod.  I think there are third party utilities that can help me save her music, but I was hoping someone could explain what Apple does and doesn't allow when an iPod user get's a new computer, and any advice on what utility or instructions, on how to save her music.  I don't really understand the problem, so if I could at least understand what Apple does with their proprietary devices and software, hopefully I can better resolve the problem.

Thanks