Hi Andrew,
I am an F1 student and I received my EAD through optional practical training on November 19, 2008.
As far as I know we have 90 days unemployment period. Here are my questions;

Q1 - Do I have to notify my school or Department of Homeland Security that I have a job now? because of 90 days.

Q2 - Now I have a contract with H&R Block to work as a tax preparer and this is a seasonal and part time job, but I have not actually started working in a certain office yet, I am still waiting for them to contact me and tell me which office I will work for, but again I have a contract with them, my contract states that I was hired on January 20, 2009, so will this contract postpone that 90 days unemployment period?
Thanks very much