Dave,
The only printers that are fully compatible with AirPrint at the moment are:
HP Envy eAll-in-One series (D410a)
HP Photosmart Plus e-AiO (B210a)
HP Photosmart Premium e-AiO (C310a)
HP Photosmart Premium Fax e-AiO (C410a)
HP Photosmart e-AiO (B110)
HP Photosmart eStation (C510)
HP LaserJet Pro M1536dnf Multifunction Printer
HP LaserJet Pro CM1415fn Colour Multifunction Printer
HP LaserJet Pro CM1415fnw Colour Multifunction Printer
HP LaserJet Pro CP1525n Colour Printer
HP LaserJet Pro CP1525nw Colour Printer
In addition, six more HP printers will become AirPrint capable after a firmware update on December 27:
HP Officejet 6500A e-All-in-One
HP Officejet 6500A Plus e-All-in-One
HP Officejet 7500A Wide Format e-All-in-One
HP Officejet Pro 8500A e-All-in-One
HP Officejet Pro 8500A Plus e-All-in-One
HP Officejet Pro 8500A Premium e-All-in-One
Although AirPrint will only permit printing to these select HP printers, Apple has said that compatibility will eventually extend to printers from other manufacturers. However there will no doubt be Apps etc that will allow printing to other wireless printers pretty quickly.
Unfortunately mate that's all i know about it at the moment as it's not something i have looked into in great detail yet