This is what you are looking for:
http://www.cnc4pc.com/Store/osc/product_info.php?cPath=25&products_id=155.
We also have a new version of that same circuit:
http://www.cnc4pc.com/Store/osc/product_info.php?cPath=25&products_id=155 .
It goes between the PC and a basic breakout board or parallel port drivers, such as HobbyCNC, G540, Xylotex or Rockcliff. Since it provides Safety Charge Pump, buffered signals, and terminals for inputs it can really enhance the setup of any router based system.
Arturo Duncan
http://cnc4pc.com