Hi Dan,
This may be off the wall, but check the OS X side to see what DNS machine it may be referencing. If it's not referencing a valid DNS provider, it may not be able to find Amazon...although you should then be finding it hard to reach other places too. Since you can reach Amazon from Classic, it has to be some setting in OS X and DNS info seems most likely. You might need to check with your ISP and see what DNS server you should be trying to talk to.