I'd given up hope of being able to wireless print using my HP 5600 plugged into USB port of my Airport Extreme. I can see and connect to the printer, when I print, it goes into pause mode, and when I unpause, it shoots blank paper through the printer.
If I connect same printer via USB to my new Airport Express, it works like a champ.
Does this even make sense? I'd really like to use the Express in my living room for playing music, but I also want wireless printing.