AirPrint and Dell Printers

"AirPrint requirements
To use AirPrint, you need one of the following devices running iOS 4.2 or later:

iPad
iPhone (3GS or later)
iPod touch (3rd generation or later)
You also need a printer that supports AirPrint. That printer must be connected to the same network as your iOS device.

Here is a list of printers that support AirPrint:

Model
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 (D110)
HP Photosmart Wireless e-AiO (B110)—Europe and Asia-Pacific
HP Photosmart eStation (C510)
HP LaserJet Pro M1536dnf Multifunction Printer
HP LaserJet Pro CM1415fn Color Multifunction Printer
HP LaserJet Pro CM1415fnw Color Multifunction Printer
HP LaserJet Pro CP1525n Color Printer
HP LaserJet Pro CP1525nw Color Printer
HP Officejet 6500A e-AiO
HP Officejet 6500A Plus e-AiO
HP Officejet 7500A Wide Format e-AiO
HP Officejet Pro 8500A e-AiO
HP Officejet Pro 8500A Plus e-AiO
HP Officejet Pro 8500A Premium e-AiO
"


http://support.apple.com/kb/HT4356

Contact Dell customer or technical support to ask if they have any plans to include support for Apple's AirPrint feature with this printer or with any of their printers as HP has done being first to do so.

Make sure the sharing is checked on the main computer otherwise it won't share. Sometimes you have to change firewall settings also.