Candice:
If you do it yourself, you need to complete Form 1040-ES to determine your tax liability, then mail the quarterly estimated taxes NLT than the 15th of April, June and September 2006 and January 2007. You also should send in a quarterly estimated tax payment to your state (assuming you live in a state with an income tax).
You can download the Form 1040-ES from the IRS website (
www.irs.gov).