It appears this tweak is no longer working after users upgrade to iOS 5. We have found an alternative solution that will work with iOS 5 and Windows.
AirPrint is a major feature of the iOS 4.2 upgrade but is limited to only eleven printers.
Now thanks to a simple tweak from elpamsoft.com, Windows users can use AirPrint with any printer on the same Wi-Fi network as their iPad.
Open “Printers” in the Control Panel, right click on the printer and click “Printer Properties. Click the sharing tab and share the printer.
*If your having problems with the iOS device discovering your printer, try rebooting your PC or restart the Bonjour & AirPrint service by going to Start > Run > (type) services (Click OK) > Right Click “Bonjour Service” > Click Restart. (do the same for AirPrint Service).
If you would like to check the status of the print job or cancel it, double-click the home button, tap the Print Center icon, then select a print job or tap Cancel Printing.
Enabling AirPrint on a Mac is simple, here is a step by step guide.