Pel, I thought you were a lot older than high school age! I thought you were like, 25 or something. You learn something new every day, I guess.
Anyway for boarding school you have to think about all aspects of your life. The rules are going to be different, and you have to follow them all the time, instead of between 9 am and 3 pm. Also you have be more independent, like you have to be able solve your own problems and do your homework without your mum telling you that you can't watch TV until you do your homework! (I got that one a lot). So if you think that you'd be okay without your parents there to help you (and trust me, I'm 19 and I still don't think I'm ready to move out), and still be okay with the rules of your school, you should be fine.
A lot of boarding schools don't let high school students have internet in their rooms. That would be a big thing to think about when choosing a school, since you're obviously quite involved with internet communities and stuff, and the school computer labs might not let you use IM or post on message boards.
Just make sure when picking a school that you do a lot of research on the school, and have a list of questions to ask if you go tour the school, so that you don't get there and find you're living the next nine months without the internet except for school projects!