At the time of this writting here are only a handful of printers from HP that will work with the native print function in the ipad device. Following these directions will allow you to share a printer from your computer to the ipad.
Windows:
http://ipadhelp.com/ipad-help/how-to-enable-airprint-for-windows-and-use-any-printer/
Mac:
http://netputing.com/airprintactivator/airprint-activator-v2-0/
