In order to print from an iPad your printer needs to be "Airprint" compatible which, in effect, means you have to have one of a small number of models of HP printer.
There is a Windows app you can buy (it costs about $10) called "Fingerprint" which will apparently allow you to print to any shared Windows printer from the iPad. I have no experience of it personally, but it seems to receive favourable reviews. See:
http://www.collobos.com/index.html