Mac OS X 10.6.5 only: The latest OS X and iOS updates were supposed to enabling Air Printing, or printing from iPad/iPhone/iPod devices, but support was dropped along the beta path. We found a manual workaround, but this small download is easier.
Download the AirPrint Hacktivator, un-ZIP the application and run it. If your OS X or iTunes downloads are out of date, it will let you know. Otherwise, there are two buttons to "hacktivate" AirPrinting on your system, so that iOS 4.2, when it arrives on your devices, will offer printing via your Mac.
AirPrint Hacktivator is a free download, requires the latest 10.6.5 OS X update.