I don't think it will work with Airport Express-, Extreme-, or Time Capsule- attached printers. The bottom line is that unless the printer is AirPrint compatible, the device sending the print job to the printer must have a locally installed printer driver. You cannot load a printer driver on Airport Express, Extreme, or time Capsule. Neither will you be able to load a printer driver on an iOS device.
The more I think about AirPrint the more I dislike it. Apple should have allowed to install printer drivers on iOS devices for printing to traditional printers and leave the option for AirPrint open for new printers.
I can print to my 4 year old HP printer using airport express on the HP photo print app without any computers turned on. Where are the drivers here? Built into the app?