Sorry, let me clarify...
Ipods only charge when connected to a computer through a POWERED firewire port. Some have reported problems that if you do a high volume synch (e.g., 10 gig), the synch can drain your battery if u have an unpowered port and start without a fully charged battery. Writing to the HDD is a big power drain...apparently far more than just reading.
No need to fear though. I've had my new 30gig die while connected. I also once had my XP system unable to recognize the IPod to safely eject. In both cases, after the battery died, I disconnected, charged, reset, and in my case re-created folders (notes, contacts, calendar), with no lasting problems.
Now, I only synch the pod with a strong (3 segments) battery charge.