I think that Puncia pretty much summed up what I was going to say. The best way to find out if someone will be accepting is to tell them that you are bi/gay first and then see how they react. If they react poorly, then it's obvious that you should not tell them about your feelings for them, as it may make them uncomfortable.
It's a sucky situation to be in, as I've been there myself, but it's also something that sometimes turns out okay in the end. Just take it slow, do not do anything brash and word wont get around the school as fast as you think it will.