I'd agree with Ted's synopsis of the two.
Getting even deeper into it, I think hip hop should be held to a higher standard than rap. A lot of things are called rap but aren't really hip hop. 50, Mike Jones and others rap... but they aren't hip hop. Hip hop is a purer form of the art; it's about the expression, not the money; it's about the message being conveyed, not the rims and the ice of the messenger. I don't want to go too far with this, but it's almost as if Lost is rap and Found is hip hop. I try to be really careful about what I refer to as hip hop.
It's hard to explain, but if you want a definition of hip hop, rent Brown Sugar.