Reply to Richard: I don't know if it matters to you and we're clearly on the same side here, and certainly my speculations about causes are no more than speculation - I know nothing about printing protocols or networks.
But as a matter of face my set up has nothing to do with Windows at all. I have a Mac Mini, an iMac (both on Snow Leopard), a Netgear router and WiFi extension and a Canon printer. The old HP worked fine wirelessly. The Canon get's a communication error if the iMac is wired to the router via Ethernet. I either have to have the iMac's ethernet cable unplugged, or the printer plugged into the iMac via USB.