Not in the traditional sense.
In the traditional sense, terrorism isn't a cross-border phenomenon. E.g. The Red Brigades, Bader-Meinhoff, and even the IRA didn't operate across (more than one) border(s). They were domestic terrorists.
Al Qaeda is different. It's closer to the Barbary Pirates than to a traditional terrorist organization.
As you say, traditionally, states-of-war can only exist between governments.
The [link|http://www.luminet.net/~tgort/tonkin.htm|Gulf of Tonkin] resolution was probably closest to the 9/14/2001 resolution. It didn't state that the US was at war with North Vietnam, but it authorized the use of military force to repel and prevent further aggression.
I think if we apply the Duck Test, then the 9/14/2001 is a declaration of war. YMMV.
Cheers,
Scott.
