Just out of
curiousity, do the USB-parallel adapters support all the
 low-level bit-twiddling that you can do on a real PC printer port? Can
 you treat them as 12 digital outputs and 5 inputs? 
 Nope,. They generally appear as a DOT4 printer device; in other words,
 they make a parallel printer appear to the system to be a USB printer,
 not the USB port appear to be a parallel port. 
 
Right... Pity...
 But if you need the port, what's wrong with a Centronics parallel port
 or a couple of RS232 ports on a PCI card? They are the "real thing",
 AFAIK. 
Nothing, provide the host machine has a PCI slot. There seem to be an
awful lot of modern PCs that have USB as the only expansion.
-tony