It's definitely possible.  I was a high school drop-out and later entered a BSN program.  My first piece of advice is to know what you are getting into.  Getting into an RN program involves a fair amount of bulls*** so be sure it is something you want to do.  Secondly, make sure you talk to students in the program to see what it is really like.  This was my fatal mistake.  I trusted my school's administrators that my program was very clinically oriented and academically rigorous.  I ended up dropping out because of how completely untrue this turned out to be.  (No worries though, I'm now in grad school at an Ivy League university and I love it!).

Now, as far as how to get in, if you never took the SATs or ACTs you will probably have to start at a technical college.  They may or may not require a GED or HSED, but will probably require some sort of placement testing.  Depending on you placement level, you may have to take remedial classes.  If you are planning on entering an associates degree program, keep in mind that many have long waiting lists, so don't go trying to cram all of your prerequisites into one or two semesters if you don't have to.  Take your time, and go into the classes well-prepared as grades are far more important for nursing school admission than any other factor.

If you want a bachelor's degree you have two options.  The first option is to go through a traditional 4-year university program.  This would likely involve applying to the university as a transfer student after completing a certain number of credits (generally 24 which is the equivalent of two light courseload semesters).  If you have a specific university in mind, be sure to contact them ahead of time to make sure the courses from the technical school will transfer and satisfy the university general education requirements.  After being admitted to the university you will probably need one more year of coursework before applying to the clinical program (the application to the nursing program is generally a separate process from applying to the university).  You could also do 2 full years at the technical college and apply to the university and nursing program simultaneously, but this might hurt your chances.  Either way, be sure to check with an advisor in the nursing program to find out what prerequisites you need. Generally you will need some courses in chemistry, microbiology, anatomy and physiology, and psychology. 

A second option is to get an associates degree and then do a BSN competion program, many of which are online.  These programs are generally a better financial option because you will be able to work as an RN while finishing school and many hospitals offer tuition reimbursement. 

As far as where you go to school, if your goal is to work as an RN it really doesn't matter, they'll take you.  Anyways, I know this sounds confusing, and it is for a very good reason.  Nursing schools get far more applications than they have space in the programs; so this is their way of weeding people out.  Hope this helps.  Good luck.

THAKS, THIS HELPED ME ALOT...I'M IN THE SAME SITUATION, NOW I KNOW WHERE TO START=)