This may sound like a stupid question, but what make/model is your printer?? Not all printers are capable of being "shared" via USB printer port, like on the NAS.
Case in point, I was excited about the thought of finally killing a few birds with one stone by having a designated NAS device, and finally sharing our one printer amongst an XP desktop and laptop and Win7 laptop...
After countless hours of frustration, conclusion was, my printer, a Lexmark z515 was not capable of being "shared" in that way. I may be wrong, but that's what I've learned.
If someone can prove me otherwise, I will be eternally grateful.