IPP Printing, frustrating

Hello folks, first time poster here.

The scenario is this: I have a Canon imagerunner 2200 at my office. It sits behind a router, and I have ports 9100, 631 and 515 currently forwarded to it. The printer has a static LAN IP. The router ip is not static, but for the moment that's a moot point.

I can access the remote ui for the printer from my browser using the ip addy:631. There is no print server, as this Canon has it's own network card and IPP support.

I cannot, however, print to this printer from offsite. In fact, from the properties section of the printer that I've installed, I cannot even get the printer to respond to a request for system information.

I've set the printer up by defining a port like I did for my computers on the lan (they all work fine with the printer), and I've also tried using the printer wizard's setup for "a printer on the internet" but it rejects the ip (and the ip:631) out of hand. I'm confident that I've the correct PCL drivers as well. Any guidance? There's very little info on the net about IPP, and what I've found always assumes the presence of a dedicated print server.

Client-side I'm running Win XP pro, fully updated.