Caveat: I believe the followings are correct to my knowledge but you should check with your CPA.
You pay estimated tax by 4 installments:
Q1 2010: due Apr 15, 2010
Q2 2010: due Jun 15, 2010
Q3 2010: due Sep 15, 2010
Q4 2010: due Jan 18, 2011
http://www.irs.gov/pub/irs-pdf/f1040es.pdf...