You might want to check out this post yesterday.
 
http://www.fivedoves.com/letters/sep2007/shabach96.htm
 
It will be a bio chem attack and will involve 5  major US cities. A very, very strong attack. Houston being a harbor city suits their goals well by maximizing the effect. The other 4 I would also suspect to be on the coast. When will it happen?  soon enough, this fall most likely.