I'm not 100% sure but I seem to remember that Mac formatted HDD based iPods (such as the 3rd gen) are formatted in the HFS+ format which is not readable by any flavour of windows. In which case the only way to use the iPod with the windows machine is to format it. There are plenty of utilities for both Windows (XP and Vista) and OS X that will allow you to copy files off another persons iPod, but thats only if the underlying format is compatible with the operating system in question.