I think the big issue is that the more recent Macs have a Firewire 800 port, but that the first several iterations of the iPod were only Firewire 400. OP, if this is the issue you are running into, then you can either get a FW400-->800 adapter ($10-$15), or, if you happen to have an external hard drive with both types of ports on the back, just daisy chain your iPod through it. That's what I used to do with my 3rd gen iPod.
EDIT: Sorry, just looked at your signature and noticed that you have a MacBook Air, and thus no FW port. Not sure what to do in your case.