Firstly, I doubt the Arab world would embargo everyone, since they want to sell their oil as much as we want to buy it. Our economy would screech to a halt as fast as theirs would (the U.S. uses something like 25% of the world's oil and the Middle East produces something like 37%). If they just embargo the U.S., we could buy all our oil from other sources while the European buy Arab oil (the market will just shift). Of course, if we seized Iraqi oil fields, it really wouldn't matter if they wanted to embargo us (assuming they didn't mine all the waterways, which would bring about a nice little regional war). Eventually, we would open new wells in the Carribbean, Alaska, and gain access to the extensive Siberian oil reserves.

I don't think any terrorists are going to make a massive electro-magnetic-pulse that destroys all the computers in the world. That sounds like a scheme from COBRA at best. Even assuming that it could plausibly be done with ballistic nuclear warheads, there are very few countries with that many warheads, fewer with ICBMs and fewer still that would launch them at us or let terrorists steal them. We could probably also shoot down a limited number of warheads, so I suspect they would have to launch a heck of a lot to hit much of anything.

-Biscuits