According to the wikepedia as of 28 May 2010 there were 31 states with a "castle law" or "castle doctrine". Nebraska was NOT one of them.
Arizona IS one of them but it did not help a certain young former US Marine in Tuscon.
Do an on-line search of your state code to see what is the current status.
The "castle doctrine" is an item the US inhereted from our English common law background. It does vary from state to state and has some limits. It is best to do your homework before you open fire !!!