Chefsint,
The federal minimum wage is $7.25 per hour effective July 24, 2009, so any hours worked on or after 7/24 by employees who are paid minimum wage would be paid at $7.25 per hour. For instance, if the pay period runs from 7/20 through 7/26, regular time worked 7/20 - 7/23 would be paid at the earlier rate, and regular time worked 7/24-7/26 would be paid at $7.25. To make it easy to handle overtime, I would tend to pay it based on the new minimum wage.
I hope this helps.