How does "interrupting" work?

I played a meta-phsyicist for a few levels and I noticed that I would ocassionally get interrupted while casting. Same with a Doc that I played for a little bit. Since I am accustomed to the idea of "spells" being interrupted while "casting" from playing other games, I thought nothing of it. (Although I do wonder what skill affects the chance of interruption.)

Anyway, I was playing my adventurer last night and decided to use pistols (I think they look cool!). I got two very nice pistols that fire very very fast and I'm happy with them. I received a mission for a pistol that did far more damage but was about twice as slow. I decided to try it out, and here is what I discovered.

I noticed that although the fight still lasted about the same amount of time (the mob didn't die any faster with the slower, harder weapon), I took far more damage while using the bigger, slower weapon paired with one of my fast weapons, than when using two quick weapons. After a while it dawned on me why. It looks like the quick firing of the fast weapons was somehow preventing the mob from firing/casting at me, and thereby preventing any damage. I would have about 10 lines of "You hit so-and-so for ## points of projectile damage!" for every one time the mob shot at me.

Was I interrupting the mobs?

(This was happening on both caster and melee/ranged weapons mobs.)

IF I was indeed interrupting them, then that must mean that I can also be interrupted, which makes me wonder what skills affect my chance to be interrupted while firing a gun?

Can anyone answer this question?

And is it possible to continue negating damage like this at higher levels? against higher mobs? (there were several fights where I did not take any damage at all, because the mob never actually fired on me, even tho it kept trying to) Does this trend continue at the higher levels?

Is this an effective tactic in PvP? Can you just continuously interrupt your target, plinking away thier health?

I hope someone can answer these questions. =) Thanks!