There are many more qualified libertarians out there to answer the questions, but I will try my take on them, because I think it to be important to sharp your own opinion.
Ok, let's start.
1) When, if ever, is preemptive war is justified?
There is no way that a preemptive war is justified, as much as there is no way that a precrime (from the movie Minority Report) is possible justified. A preemptive war is acting against a suppossed and even imagined threat by some other state. Whenever a state acted on such a belief(like Adolf Hitler), and no, it is just a belief and no fact, because the "Act of Crime" did not take place in reality yet, it turned out to be wrong and overreacted or outright evil.
I hold it with Sun Tzu's principles of War, who sees negotiations (diplomacy) and assassination as better possibilities and so do I. Lately, the latter has been lost in the minds of the military, but in times of the War against Terrorism it could be usefull. After all, isn't it a more just application of justice than a war against civilian people, who never had a hand in the evil deeds?
2) When, if ever, is the United States justified in removing a foreign dictator from power?
Whenever the dictators are a considerable threat to the security of the USA and its citizens, but then you call it an aggressive war and not an preemptive strike, because it truly is that.
Also, I don't know whether there is in general an obligation to the USA to remove dictators from power, because it usually is the objective of the people who live in those countries. Perhaps those people like to have a dictator. Also, the US can always respond to pleas by those citizens, if the dictator mistreats human rights as defined in the US constitution. I see this as perfectly legitimate as long as the people, the senate and the house allow such actions.
However, such an act of liberation may not followed by any kind of occupation of the liberated country or any claims from the US to this country. Otherwise the goal of the mission is tainted, because the USA would act as an invasor rather than a liberator.
3) Do you agree with the position—recently quoted approvingly on this blog by Dr. Kuznicki—that Islamic terrorism is not a serious threat, but a hobgoblin used by the Bush Administration to increase its authority?
Yes, because the amount of attacks against US facilities and the people living in the USA has decreased a lot (well, to actually nothing). The only American deaths connected to terrorism are currently in the Middle East in the cities of Iraq, the country the USA is occupying atm.
4) Precisely what (if anything) do you propose the United States do about the Iranian nuclear weapons program?
Nothing, because there is no safe strategy to invade without destroying the growing public liberation movements and their pro-US sentiment. If all, the war against iraq has decreased those hopes a bit more.
Also, there are sound political reasons why the US won't risk an attack on the Iranian nuclear program, which are said elsewhere. Last but not least, there is no use of economical embargos, because they never hurt the ruling class but all the poor men and women in Iran, who never denied the Holocaust with one word.
5) Do you believe that the United States should defend Israel, either militarily, by the sale of arms, or in other ways (please specify)?
If called upon and validated by the Senate and the people of the US, I think it is ok for the US to help Israel against invading forces. If those preconditions are not met, I would have to decide from case to case. It is rather a hard, but imaginative situation.
6) Can you name a specific case in which an American dissenter, not actually affiliated with a terrorist organization, has been jailed or otherwise deprived of civil rights under the PATRIOT Act?
Yes, there are several such cases of arrests without actual connections to a terrorist organizations. Some students have been held hostage and also a German Arab is held hostage in Guantanamo. I can't fully trust the letter case, because the US military won't give much clues about the name or the background of this Arab/Muslim. I think therefore, we won't even know how many cases there are. This is one of the primary problems resulting from the Patriot Act.
7) Do you believe that we ought to remove American troops from Iraq immediately, regardless of the consequences to Iraqis?
Yes. It is not the Iraqis the US troops are obligated to serve, but the US citizens and nobody knows what is in their interest, because they haven't been asked (one problem that is written in the US constitution).
8) With regard to interrogation or incarceration: do you believe that infringements of religious sensitivities (e.g., mistreating the Koran) or personal sensibilities (e.g., making men wear women’s underwear on their heads) ought to be regarded as comparable with physical torture?
This is a difficult question, but I think there is a line between physical torture and psychological torture. However, as long as they are not judged by a court, I'd take care of their personal sensibilities and even their religious belief. However, I wouldn't think of it to be as important as abstination on physical torture.
9) What, if any, legal consequences do you believe flow from a declaration of war?
That the senate/house and the people are heard before starting a war with the taxpayers money as the funding. On the other side, defensive wars are always justified, because they only follow the objective that is given by the constitution: Protecting the US citizens.
10) Do you believe that the Bush Administration purposely manipulated intelligence information in order to persuade the Congress to authorize military intervention in Iraq?
Yes, I think so, because there haven't been any other options, although in real there are. Iran, Syria, North Korea, Egypt, Palestine and other Islamic or dictatorial countries have been eager participants in terrorism and even more so than Iraq, whose relatively secular Saddam Hussein always had quabbles with his Iranian neighbours (theocracy).
Also, I think the War against Terrorism ended when the US invaded and liberated Afghanistan, who were the true source and basis of Al-Quaeda.