urgent: on f1, resigning and H1-b starting October 1

I am in F1 visa ( OPT Stem extension) valid till November 2013 and have H1-B approved, beginning October 1.
I want to resign from my job, and If I stayt on F1, I still have 80 out of 90 days to find new job( which I want), while with H1b, there is no grace time.

  • So, resigning before October 1, what would be my status after October 1?
    Do i loose H1B and stay on F1?
    Is it binding upon my current employer to withdraw H1-b as soon as I resign , and
    can they still do it now after H1-b has been approved?

  • If i resign after October 1, Then what happens? If I have status changed to H1, do I have some grace period to find new job.

This is extremely urgent ..plzzz help.