Are they all terrorists?

A National Review article quoted in Eschaton says, among other things, “if my information is correct, the terrorists now have anti-tank weapons, which we may see in action in the near future.”
It seems to me that people wielding antiaircraft missiles and anti-tank weapons against soldiers may be called insurgents or guerillas or even soldiers, but what makes them terrorists? Terrorists target civilian populations, right?
Yes, there are terrorists in Iraq, clearly. Attacking the UN and the Red Cross/Red Crescent, and hotels in Baghdad clearly falls into the category of terrorism. But as far as I can gather, there seems to be a kind of transitive law at work here. If any of the people attacking us and opposing the US operation are terrorists then they all are, and if a terrorist does any kind of attack, then that attack is apparently terrorism.
To make it clear to the wingnuts out there, I deplore the tragic deaths of our soldiers in Iraq, as well as civilian deaths and any carnage at all, for that matter. I do not excuse any of it. I am just troubled by the way the term terrorism seems to be expanding to cover a wider range of anti-American military behaviors.