Printing to Windows Server shared printers from an iPad
Ignore the offical advice from Apple, they just want you to splash yet more of your cash on a licensed AirPrint printer. Here's the good news. Even on iOS5 (and iOS6), most printers can be AirPrint enabled via Windows without buying a new printer. Here are two ways to get what you want.

Free solution (requires tinkering)

If you don't mind doing a bit of configuration legwork, get JasonHD's fantastic AirPrint Installer from the MacRumors forum: http://forums.macrumors.com/showthread.php?t=1293865

AirPrint Installer is fully iOS5 and iOS6 compatible. The first post in the thread contains a link to download the software; the rest of the thread has tips for troubleshooting if you can't get it to work.

Paid solution (just works)

On the other hand, if you're a technophobe and don't mind a small outlay... get FingerPrint:
http://www.collobos.com/

Costs $19.99 and has a free trial so you can confirm it works with your printer.

Either way, you should be AirPrinting without a new a printer in no time...