I struggled on this one for a while. My printer (Epson 2200) is hooked up to my main Windows box and shared so my wife and I can print to it from our Windows laptops via wireless.
I could find and add the printer in the Mac printer setup but it wouldn't work. I was getting NT_STATUS_ACCESS_DENIED.
Searching the web found many people with the same problem. I eventually got it working by using the Advanced printer setup (a little tricky to find) and using a URI of:
Judging by what I found on the web this has been an ongoing problem with OS X. I wonder why it hasn't been fixed?
Funnily, my copy of Windows running under Parallels on the Mac had no problem connecting to the printer.