Code
arduino-timerone
This library is a collection of routines for configuring the 16 bit hardware timer called Timer1 on the ATmega168/328. There are 3 hardware timers available on the chip, and they can be configured in a variety of ways to achieve different functionality. The development of this library began with the need for a way to quickly and easily set the PWM period or frequency, but has grown to include timer overflow interrupt handling and other features.
For documentation see the arduino playground page: http://arduino.cc/playground/Code/Timer1