Right now, if you have Mac OS X 10.6.5 and an iPad running iOS 4.2 GM, AirPrint’s a bit of a mess: some people are reporting that it is working, but many are not having any luck.
We suspected that it was just this sort of compatibility problems that caused Apple to scale AirPrint support back to AirPrint-compatible printers at the last minute, but developer Steven Troughton-Smith has some instructions on how to bring it to your Mac under OS X 10.6.5 and iOS 4.2 GM.
The files you need are:
If you migrate those from a 10.6.5 prerelease build (there seem to be many floating around torrent sites and file sharing sites – build 10H542 works; naturally I can’t link you to the files themselves, sorry!) to your machine you’re just one step away from having AirPrint working.
The final key thing is you have to remove and re-add your printer in the Print & Fax preferences pane. Once you do that (and share your printer in the Sharing preferences pane) it should show up on any iOS devices that support AirPrint.
Your mileage might vary here. Frankly, at this point, the AirPrint situation is so confusing and burdened with so many conflicting reports that we’d just advise everyone to sit tight until Friday, when iOS 4.2 Final drops and settles the question of AirPrint-support once and for all.