my shop just got a new CNC router that runs on MACH 3. when looking for a computer i have heard that people have been having trouble getting the 25 pin parallel port cards to work.
so i need recommendations on what you have tried. also how hard is it do upgrade from Mach 3 to Mach 4 (as in hard ware changes) ?

requirements
9-pin serial port
25 pin parallel port
$0 - $900 total