I have tried adding an HP LaserJet 6L printer via Printer Setup Utility many times, and I always got the USB device to show under the default browser, but I could not add the printer. So I went to More Printers (holding down the Option key), clicked Advanced, and tried selecting USB Printer. This brought up usb://, but I could not find address using System Profiler or USB Prober.
Anyway, my grandson comes in, and asks "what's that Unknown button right at the bottom of the Advanced panel?" So I click it, and it comes up with a URL: usb://Unknown/Unknown?serial=0. I tried this, using the Gutenprint HP 6L driver -- and it works perfectly, even waking the printer if necessary.
This works with OS X 10.4.11; hope it helps others -- I googled for help on this, but didn't find anything on the subject.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20081003015811305