As the others have stated, the answers to your questions all depend on whether or not you are a 501(C)(3) group, what your Bylaws state, etc....
If you are a 501(C)(3) then likely your Bylaws (if you have them) will indicate that total control of the decisions and organizations of your group are by your Executive Board and/or through a majority voting taken at an offical meeting and put up for motion by your President (or something similar).
My group's Bylaws actually state that only the extecutive board has the right to vote, and only a PTO member (parent of a student or staff member at the school - not the Principal) can be voted into a position of this nature. But again it all depends on what your Bylaws state.
If you are independant, but don;t have Bylaws then you and your other members should sit down and define your Bylaws. Define evenything, incluidng elections, terms of office, a quarum, who votes, control of funds, etc.
If you are independant then your executive board has the right (again, based on Bylaws) to hold meetings anywhere you want, to allocate funds for anything you want and to define the voting process.
At my school we had a new Principal last year. As the new PTO President I set up a summer meeting with him to outline my priorities, to go over our plans for the year, to hear his priorities and to explain what has been done in the past and what things we would like to change. Effectively I set the precedence that this PTO is not controlled by the Principal, but that we want to work with him to make the school better for our children.
If you think about it a Principal would have to be an idiot to alienate their PTO. A PTO can do so much for a school, so why ruin that. But, if the existing precedent is that the Principal has control, then why would he ever relinquish it? You need to answer our questions about being independant and your Bylaws and then go from there.
If things turn out in your favor regarding being independant then something needs to be done. Who was defined as the PTO President for the year? Was this the same person as last year? Is it a staff member or a parent? Was there minutes written regarding these elections? And using your Bylaws can you "challenge" the elections asking for new ones?
Worst case scenerio, and it seems that this might happen, you may need to go to the Principal's boss. This may be the Superintendant of Schools or the town's School Committee. Either way try defining things first and then talking with him and/or the other parents and see if an ammicable decision can be made.
Good luck, PresidentJim