Apple has posted a Firmware Update for the latest generation of iMacs.
This update is for 20-inch and 24-inch aluminum iMac computers with the ATI Radeon HD 2600 Pro graphics running Mac OS X 10.4.10 with iMac Software Update 1.2.1 or Leopard with iMac Software Update 1.3.
It updates the graphics firmware on the ATI Radeon HD 2600 Pro to improve system stability.
For detailed information on this update, please visit this website: http://docs.info.apple.com/article.html?artnum=307008
The update weights and is available either through the Software Update utility or through Apple's support web site [1].