This site has a step-by-step process to set up printing from an iOS device to a networked Windows printer, but someone wrapped them all into an installer called AirPrint for Windows (x86 & x64) v1.3. There’s a good discussion of printing from iPad to Windows networked printers here. Finally, an app that runs on the iPad that lets you do the same. Costs $10 and runs on Mac and Windows. Reviews were good.