canadian visiting the us but wants to change status to F1

Hi,
;Pls I am a new poster here and if anyone can pls answer this very important question for me, i will appreciate it.

I came into the states to visit my us citizen sister back in October and while here, was able to secure admission into one of the schools to study Nursing which I was not able to get into in Canada. My question is since classes start in Jan 2012, how would I be able to change my status to a student.
By the way, I drove through the border and did not get stamped on my passport. No 1-94 and the office to waved me through.

What is my best option to stay and complete the school process. My sister is prepared to sponsor me for my education.Pls help. I need an answer asap

You need to finalize tour admission to the school, and then go to the border (just before school starts) and be admitted on F1 status.