simulation of lpt interface
Usually, you can't just use 378h, because the USB device works just as a printer port. Usually it's just for printing and doesn't support full range of original LPT features. But you can buy a real 378h parallel port on a PCI card.

Look here: Writing to a Parallel to USB convertor

Also note that it is not possible to directly write to 378h in Windows 2000 and later, because direct access to hardware devices is prohibited. This policy is enforced by the CPU and if you try to write to 378h you get something like an access violation exception.