The average take-home salary of a neurosurgeon is nowhere close to $700,000. Of course, there are some neurosurgeons making this much, but these guys probably have a very establish practice, and have been doing it for quite a long time. A newly trained neurosurgeon will most likely never see this much money. Another factor you have to consider is that reimbursements for medical procedures are constantly getting slashed. Salary's are definitely dropping, at least against inflation, if nothing else (depends on speciality, location, etc...). There's also a huge movement in this country to go to a more governmentally controlled healthcare system, and this will undoubtedly lower your salary as a physician. By the time you actually enter medical school and beyond, the salary outlook for docs will be vastly different. Nevertheless, I think it’s very good that you're actually thinking about this sort of stuff while only in high school. Just make sure to get good grades and get some extracurriculars in there, so you can get into a good undergrad school. There should also be some more informed websites and forums out there that may be able to better answer your questions.
Edit: I just noticed the original post was from 2008, so the OP may not even be around anymore. Oh well, in case anyone else was curious...