Today, Apple released Mac OS X v10.6.5 which was supposed to bring AirPrint to any printer connected to your Mac. Only problem is, a last minute issue (due to patent trolling?) has caused them to pull support for AirPrint in OS X.
Don't panic! You can return it, but you're going to have to pull some files from a prerelease version of 10.6.5.
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.
Nerdy extra info: Basically, doing this should add the image/urf mimetype to your shared printer, and a new Bonjour field 'URF'. Once you have those, it should work. Theoretically, there's no reason someone can't write a server application that broadcasts said Bonjour info and prints for you, so you don't have to use files from a prerelease build. I would expect something like that to appear over the next few weeks.
Thanks to Patrick McCarron for helping me debug this method