I think you have asked a very important question. You got some great answers from the forum. But I wish to share some of my thoughts with you and the rest. I had this problem bothering me for years. In Sri Lanka Sinhalese and Tamil had a 30 year war and many lives were lost. They are mainly Buddhist and Hindus. Then there is a big problem in Tibet. Should Tibetans take arms against mighty Chinese?
I realise that there is no general straight answer to this question. It depends on the situation. So I came up with my own problem solving formula. You can use this in any situation.
A) Ask the question “What is my life time goal which I need to achieve? How my action will effect achieving my goal?” In my case I need to attain Nirvana in this life. So for me killing anyone is out of the question. I do not remember the last time I kill even a mosquito. Having said that if someone tries to kill me I will do every thing at my disposal to defend my self. I am not an Arahant. I still have attachment. So my enemy may get killed in the struggle. It is bad luck. Even I killed someone it will not be a hindrance to achieve my goal. Angulimala killed thousands of people but he became an Arahant. However I have to face my bad Kamma because I kill someone with defilements.
B) Ask the question “What Buddha or Arahant would have done in this situation” There are enough stories in Buddhism to provide sample answers to any situation. There are stories that Arhant got killed by robbers. I have never heard that Buddha or Arahant taking any ones life. Because you are more familiar with Christianity ask the question “What Jesus Christ would have done in this situation” Even in his crucifixion Jesus said “Forgive them. They do not know what they are doing”
C) Ask the question “Is there an alternative to killing the enemy” The war and killing is an old school strategy. By trying to kill your enemy you will give more ammunition to the enemy so he will attack you even harder. Mahatma Gandhi fought mighty empire with his none violent strategy. Now this strategy has made to an art form. Please read following article titled “From dictatorship to Democracy”http://www.aeinstein.org/organizations/org/FDTD.pdf
There is a good story. This monk converted a snake to a Buddhist. One day some naughty children came and throw some stones at the snake and the snake got injured. When the monk came back from his visit to the village and saw the injured snake. Snake said to the monk “See what happen to me. You ask me to not to kill and it seems like I am going to get killed by these boys” Then the monk asked the snake. Do you still have your fangs? Snake said “Yes” Then the monk said “ Yes I asked you to not to kill but I did not ask you to not to show your fangs”
So the straight answer to both of your questions should be “No” I do not have the right to take some one life or my own life (Suicide or euthanasia” One of the ten commandments is “Though shall not kill”