I guess you didn't read www.apple.com/.../airprint.html
my Dells:Precision M6300 - Windows 7 / Ubuntu 12.04Latitude D620 - XP Pro SP3Precision M6300 - Windows 7
There are only certain HP printers that I can find are currently AirPrint capable. I, however, found a free download on Cnet of FileHippo that installs a driver in your printers folder to print from your Iphone or Ipad. I did this using the Dell 3115cn and works great. Your computer needs to be on in order to print.
what was the name of the driver?