You don't need a laptop in high school. I got a laptop in 8th grade, a cheap Dell that cost about $1000. It was really slow, and I almost never used it away from my desk. At the time, the same money would have gotten me a fairly good desktop, and in fact I bought a midrange desktop a couple years later because the laptop was unbearably slow. That doesn't matter much these days since a 13" MBP is about $1000 and it is not much sower than any other MBP. But it still has many of the downsides of a laptop--It can't really be upgraded, and there is no expandability. With a desktop, you can upgrade the processor, add a new optical drive (like a blue-ray burner), and add all the hard drives you need. You can also cheaply swap out broken parts. An equivalent desktop is still a whole lot cheaper than a laptop.
I never took my laptop into school. There was just too much risk of it getting stolen/damaged, it wouldn't work with the school wireless network, and there was simply no need. If a class needed a computer, there would be one provided. The school had laptop carts that teachers could check out for projects or presentations.
You probably can't see anything else you might spend the money on right now, but trust me, once you buy the laptop you will want to buy something else, but then you won't have any money. I think it is good to have your own computer in high school, and if you get a midrange desktop and save/invest the rest of the money, you will probably be a lot better off in the future.
If you are savvy enough, you can build your own desktop. You probably won't save much money over getting, say a Dell, but you will learn a lot and you will have more options for upgrades in the future. Dell tends to limit the expandability of their cheaper computers, for example they might only have 2 SATA connectors, while even most entry level motherboards have 4 or more. Newegg.com is a great place to get parts, and make sure you understand what you are buying and are sure everything will be compatible. If you are not sure, ask someone (this forum is not the best place) or buy a computer already built.
If you are really set on a Mac, you might be able to get OS X to work on your desktop. We can't talk about it on this forum, but there are plenty of resources out there, and you can probably get it working if you have enough patience.