I mean, doesn't a state of war legally occur between two govenrments? (I know, the concept of "legal war" very closely approximates an oxymoron.) If so, then what "government" does bin Laden claim to be the head of?

The Islamic Republic of Moron?

And if not (that is, if a state of war can occur between a government and a private citizen or enterprize), then by extension why can't a state of war exist between two (or more) private citizen or enterprizes? Can I declare war on Micros~1 (OOOhh, now that's tempting...)

No, I think bin Laden's "Declaration of War" is just so much chest-thumping propaganda. He's nothing but a common criminal...a highly skilled, murderous, cowardly common criminal, but a common criminal nonetheless.