Writing to a Parallel to USB convertor
Most USB parallel printer adapters, even when the drivers are set up right, are not all that well suited to signaling to things other than printers.

For other parallel input or output tasks, you would likely be better served with something such as the FT245 or a similar USB IO chip.  Or else use a USB capable micro-controller and write a program to run on it which will set pins in response to USB messages. Or even a micro-controller with a USB-serial interface (such as the arduino board Majenko suggested) where you can send it a message through the host OS serial port API to set the IO pins to whatever (parallel) value you wish.

An additional factor to be aware of is that while USB can have very high throughput, it also has a quite high latency (delay) compared to old-fashioned parallel ports.  This can be very problematic in situations where the computer must really interact with external hardware, or communicate in a conversation of short messages.  If that problem arises it may be necessary to move the lowest level of the software task to a micro-controller on the far side of the USB which will have fast control of its own IO pins, and use the USB for higher level communication between that and the PC.