Access Denied, Unable to Connect Error Message

I have a printer (Canon MX310) that is connected to my iMac, which is running Leopard. I've shared it via Sy Preferences > Sharing. I want to be able to print to it using my XP laptop. When I connect to my home wireless network, I can see the printer just fine in the list of printers on my laptop. But if I try and open it or send a print job to it, I get the following error: Access Denied, Unable to Connect. This is probably a very basic problem/question. But any help would be appreciated. Thanks!

 

The printer works just fine with the Mac. It's not password protected. Also, when I try and ping my Mac, it times out. I feel like it's probably a firewall issue. But I've never 'directly' changed a firewall's rule. And I've never used the Mac's built-in firewall. Do I need to open that port up via Mac's firewall? Wouldn't that have been what I did when I shared the printer in System Preferences? How do I access/manage Mac's firewall. I tried looking for it under Applications > Utilities but didn't find it. Could it be a firewall issue on my XP laptop where the firewall isn't allowing traffic/requests out to my Mac system?