This is a very interesting thread. I think that in some respects, one might suggest that Brown's was an assault on a military target, the federal arsenal at Harper's Ferry, the goal being the acquisition of weapons for a slave revolt. He was (unfortunately) not successful.
This led me to ask might a better analogy with Osama be the slave revolts themselves, folks like Gabriel Prosser, Denmark Vesey, and Nat Turner. If memory serves me correct, at least in the case of Turner, they attempted to kill any white person they encountered - male or female, child or adult.
Was that a terrorist act? Again, I don't think so. As for Osama, I really have ambiguous feelings. As I have said before, my first response on the morning of 9/11 was that this was a case of "chickens coming home to roost" and while I feel for the families that lost loved ones, I still feel that way.