Hi Alex
Same question as Tweakie,
There is a problem with some of these USB to parallel converters, especially the cheap ones, in that they are not bidirectional, they do not support EPP or ECP modes.
In this application some of the printer port pins need to be set as inputs rather than outputs, for EM Stops and limits for example.
I have had instances of even some printers not working properly with them. Your best bet would be to use either a PCMCIA card parallel port (check is supports ECP/EPP) or a full blown USB motion controller.
Regards Mark