Aiming4, welcome to the board. Good to hear other opinions! I have to say, however, that building a portfolio or planning your investments around a potential terrorist attack in the US is probably a bit much. Not only will it happen sooner or later, IT DID, and the markets tanked big time. And you know what, it took all of five weeks for the Dow to get back to its close on Sept 10, 2001 and only eight weeks to pass that level for good.
As FF pointed out, you can't really worry about acts of God, so to speak. Your planning for things like terrorist attacks might be to keep, say, 40% or 50% of your money on the sidelines when political tensions might be rising as opposed to only 10% or 15% when you think everything is a-ok.
The .com blow-up and the 9-11 attacks are two totally different things.