Scott is right. You will need to make estimated tax payments using Form 1040-ES on April 15, June 15, September 15 and January 15.
For 2006, if you file your return by 31 January 2007, no January 15 payment is due.
He will owe a 15.3% flat rate in self-employment taxes.
How much income tax is due depends on a variety of factors, not the least of which is your income and whether you have children.
I can do a estimate for you free-of-charge if you send me your data to
[email protected].