Rough outline (I've thought of giving a talk like this several times over the last few years but it never happened):
- layered network
- packet-switched networks
- IP packets
- UDP
- TCP
- routing
- high-level view of BGP/etc dynamic routing protocols
- NAT
- encapsulation
- tunneling/hacky wierd stuff (SWANS architecture, IP in ethernet in UDP in IP in ethernet, IP in DNS in UDP in IP in ...)
How you'd fit this in less than an hour, though (talk really fast?) and if anyone would actually be interested are other matters entirely 
Major reason for such a talk: the number of people who can't fix their networks by reading the output of tcpdump should be reduced, as should the number of people who don't understand how SWANS works :P