While I am far from an iPod or iTunes expert, my understanding is that there is basically a one-to-one binding of an iPod to an iTunes instance. My music collection is stored on my Windows XP PC's disk, and this is synced to my iPod. When I first bought the PowerBook, I downloaded some podcasts to iTunes, and assumed that I could add this to my iPod. I was wrong—iTunes informed me that the only way to do so was to erase the content on my iPod. That is, one iPod, one iTunes. (Actually, I'm not sure it's strictly one-to-one—when I had my iPod replaced, iTunes made no complaints about syncing my collection to the new iPod. But the relationship in the iPod→iTunes direction is certainly one-to-one.)
I don't think this is ideal. I spend a lot more time on my PowerBook, and, for one thing, I like downloading podcasts to its iTunes instance. Basically I would like to be able to push content from my PowerBook's iTunes to the iPod as well as from the PC's. It's painful enough to transfer material over to the PC's iTunes as it is, and with DRM-protected tracks, (I assume) it's essentially impossible. That is, if I use iTunes on the PowerBook to purchase music from iTunes Music Store, it's stuck on the PowerBook unless I erase my iPod. Please, correct me if I'm wrong here.
Are my observations correct? Are there any workarounds?