Hey me too! Or that was my problem. I just got into highschool and coming out is never easy. My parents found out through my friends who posted on facebook. They were a little upset and grounded me from any sleepiness ever because they didnt want me sleeping around with other girls or guys. The people at school are mean and I came out in seventh grade so the worst year of middle got worse for me. Homophobes got annoying but it really only narrows down to a couple people who you avoid. Your true friends show and even if no one else seems to care, there are millions out there including me who care about this kinda stuff regardless of gender or age.So if you do have feelings for a girl, be bold. Caroe diem. Seize the day. Good luck!
There are good online groups for teenage gay/lesbian/bi issues. It's a tough time to come out, as you say, since there is so much casual bashing (the kind of stuff where people say "that's so gay!" as an insult) and so much thoughtless stereotyping. Do you know any adults who are gay or lesbian that you could talk to? There are also some liberal churches that have a lot of gay and lesbian members.
It might be good before you make any general announcement to go to a women's bookstore and see what kind of books are out there for teens, and read up on the subject first. That way you'll have a lot of your questions answered and probably get some good resources, too. And/or look online, for the same reason.
You could start with some of the lesbian/gay alliance sites, or even (or maybe better) the PFlag group. That's Parents and Friends of Lesbians and Gays, and even if you don't need them, your parents might. An FAQ page from PFlag, giving the questions parents most often ask, printed out, might be a useful backup for you when you do tell them.
My sister is a lesbian, and she always knew, and we always knew too, at least we knew that compared to the rest of us she was a definitive tomboy. By the time she figured it out enough to tell us, it wasn't much of a shock. I think she was about a sophomore. You might find that this is true in your family, too, even if you finally have to tell your dad that his dopey stereotyping is not that hot an idea. Love and support are the goal, and even though you might have to plainly ask him for it, it doesn't sound like his comments are based on anything but unfamiliarity.
Good luck, I hope you get some good answers here too.