Yes. I would without hesitation for self-defense/defense of others close to me (and possibly people I don't know, depending on the situation). I suppose I could kill someone for another reason, but I can't think of any where I would right now.
How? Preferably with the element of suprise (of course, that isn't possible with self-defense). Knife to the back of the head, or a bullet. I have no interest in being sadistic, death is punishment enough for whatever reason was.
I don't consider myself violent. I don't really let myself get angry to the point of physically wanting to harm someone beyond a bloody nose. However, I don't think I'd have any problem killing if it was constituted. If my life or someone elses' was in danger and deadly force was necessary, I could kill and I don't think it'd have too great of a psychological affect on me.
I'm not a fan of blood and guts or a violent struggle. I'd prefer to use a gun if I was given an option.
I'd be reluctant to kill anyone... they would have to make me feel very threatened and angry before I would even consider it, and even then I'm not sure I'd be able to go through with it if I had to do it myself (and I'd almost definitely run rather than defend any person other than myself). Does having someone else kill a person for me count? I think I'd find it easier emotionally to do that, and might well do that if the person made me feel threatened in a significant way, and I thought I could get away with it.
By whatever means possible, as matched to the deed first inflicted by the intended target. An eye for an eye: a punishment that fits the first crime committed.
You gave me hyacinths first a year ago;
They called me the hyacinth girl.
Yet when we came back, late, from the Hyacinth garden,
Your arms full, and your hair wet, I could not
Speak, and my eyes failed, I was neither
Living nor dead, and I knew nothing,
Looking into the heart of light, the silence.
I would have a seriously hard time killing anyone. But I would do it if I thught I had no other choice.
Self defense being one circumstance. Protecting friends and family members being another. Also, if I were called to serve in the military, and it was my duty to kill people, I would likely do that too.
EDIT:I don't think I would ever kill out of anger. But I get angry so little, that I really don't know how I would react. I think only duty or desperation would prompt me to kill.
Accept the past. Live for the present. Look forward to the future. Robot Fusion
"As our island of knowledge grows, so does the shore of our ignorance." John Wheeler
"[A] scientist looking at nonscientific problems is just as dumb as the next guy." Richard Feynman
"[P]etabytes of  data is not the same thing as understanding emergent mechanisms and structures." Jim Crutchfield
I put other, so I'm going to have to explain. Rules are rules.
Like most people (I'm guessing) I fantasize about killing people everyday. Usually when I'm on a quiet street late at night and there's only one other person there. Just to think if I kill that person, nobody would know for hours. I often read about serial killers, just to live vicariously through them. Sutcliffe and Onoprienko are my favourites for that.
But though it depresses me to say it, I'll porbably never kill anyone in my entire life. That whole experience has been robbed from my ready hands by improvements in law enforcement and vague human interest in the lower classes, so if one went missing, someone would notice.
CCTV, forensics, GPRS cell phones, computer systems and even fingerprinting have put a dampner on the business of killing. So of course I would kill someone if I was in danger or if someone I didn't dislike was in danger, but put me back in East End of London 1888, and I'd pick the prossies off like candy.
Why do we always come here?
I guess we'll never know.
It's like a kind of torture,
To have to watch this show.