Some people do "work their way up" because they take little steps. A lot of the time these people need to get to work faster or did not originally plan to become RNs.
I graduated last May with a BSN, a Bachelor of Science in Nursing. I went to the local university and attended school for 4 years.
Locally we have an LPN program at the Vo-Tech, as Associate Degree Nurse (ADN) program at the community college, and the BSN program at the university. Each program takes a little longer than the one before, and the more schooling you have, the more opportunities are avaliable to you. ADNs have more authority than LPNs, and BSNs have the opportunity to go into management. You can also go on and get your Masters or Nurse Practioner easier from a BSN, however I think there are some programs that will bridge an ADN to Masters. If you get your 2year ADN, there are bridge programs to get your BSN, these are sometimes refered to as RN to BSN programs.
Hope I got it all down right...
One of my classmates was an LPN for 15 years before going on to get her BSN.
As far as your high school work goes, just try to get good grades. If you have open electives math or science classes are good. Because my program was 4 years, I had 2 years of general college classes before I applied to the nursing program. Those grades are important. Community service work, Church stuff, volunteer, do things to show you think of others. The programs look beyond just grades and try to find people who are service oriented and think of others. You don't have to volunteer at nursing homes, (it would be good though!) just get out there and be a part of your community.
Ps. A 4 year program would also allow you time to go to school and explore if you really want to go into nursing.