iOS 4.2 comes with a unique feature called AirPrint which allows you to print your documents, photos, emails and web-pages over a Wifi connection with your Apple iOS device. To enable iOS 4.2 AirPrint feature on Windows, follow the step-by-step guide below. This guide is applicable to Windows 7, Windows Vista and Windows XP users.

Prerequisites:

• iTunes 10.1
• Make sure the printer is setup as a shared printer on your local PC
• Make sure you have full administrator privileges to enable/disable services on your PC

Steps to Enable AirPrint on Windows 7/Vista/XP:

1. If you have 64-bit Windows OS, go to C:\Program Files (x86) and create a new folder called AirPrint as shown in the screenshot below:




OR
2. If you have 32-bit Windows OS, go to C:\Program Files and create a new folder called AirPrint as shown in the screenshot below:



3. Download AirPrint.zip from here (Mirror) and unzip it in the AirPrint folder you created in the above steps.



4. Go to run and type "CMD" to open Command Prompt as shown in the screenshot below:



5. Now use the following set of commands respective to your OS version:

For 64-bit Windows OS:

• sc.exe create AirPrint binPath= "C:\Program Files (x86)\AirPrint\airprint.exe -s" depend= "Bonjour Service" start= auto
• sc.exe start AirPrint


For 32-bit Windows OS:

• sc.exe create AirPrint binPath= "C:\Program Files\AirPrint\airprint.exe -s" depend= "Bonjour Service" start= auto
• sc.exe start AirPrint

6. As soon as you will start the AirPrint service, Windows Firewall will prompt you allow or deny AirPrint features to be shared over networks. Click on Allow access button.

Thats it. Now open any document or email on your device with iOS 4.2 installed and click on the Print option to print the document wirelessly over a Wifi connection. [via MacRumors]

Update1: How to Enable AirPrint (Wireless Printing) on Mac OS X 10.6.5?
Update2: Download AirPrint Installer for Windows 7/Vista/XP (32-bit/64-bit)