mixing 10.2 and 10.6

I have an iBook from 2003 running Jaguar - for the last few years I've relied mainly on a work MacBook running Leopard, but I still use the old iBook frequently. The Jaguar computer is the authorized computer for my iPod, etc, but the two were friendly re: transferring files back and forth via an external hard drive.

I'm changing jobs and losing the work laptop, so I just bought the new iMac running Snow Leopard. This weekend I hooked the external drive up to the iMac and transfered everything over. Only I realized I'd still left some things on the iBook except now ... the iBook won't recognize any USB drive that has been connected to the new iMac (the external hard drive or the iPod). I have another small flash drive that hadn't been connected to the iMac yet, and it still works with the iBook so I know it's not something with the USB drive hardware. I ran Disk Utility on the iBook and it couldn't verify the external hard drive (though it did APPEAR in Disk Utility, it does not appear at all on the desktop).

Did the iMac's superior Snow Leopard self ruin the external hard drive AND my iPod from being backwards compatible with my Jaguar iBook? Is there any hope I can get things off of the iBook without buying a new external drive? Can the MacBook act as a negotiator in any way since it works with both?

Much thanks!!