Hi, I dropped out half-way through my junior year, and I started at a local university in the fall. I just got the GED and took an SAT. Colleges usually have placement tests, especially in math and English, to help you select classes to begin with. Usually with community college, there is an open enrollment policy, so getting in isn't a problem.
You may be able to get a grant for tuition by filling out a Free Application for Federal Student Aid at http://www.fafsa.ed.gov/
(They also do loans).
I recommend looking into CLEP (College Level Examination Program) exams, which let you get course credit for a lot of college classes by exam. You have to check which subjects a particular college accepts though. See http://www.collegeboard.com/student/testing/clep/about.html
There's also a similar program called DANTES.
The exact rules for getting a GED vary based on your state. They usually have information on the web. Let me know if you want help finding it or if you have any other questions.
Dropping out of high school and starting college was one of the best decisions I've made. I would have done it sooner if I'd known that I could. My performance in high school was terrible, I wasn't learning much of anything, and so on. College was a lot better. Actually, I only finished a year and a half of college at first, after which I worked for a while. But now I'm back in college. It's not perfect, but it's far better than high school was.
I think a fair number of people would benefit from this option, and it's unfortunate it's not known about more widely.