I have now tried 4 socket 775 motherboards with on board printer ports, 1 socket 775 motherboard without on board printer port (using PCI card), and dell laptop with built in printer port.

None of thease systems would work Mach3, without missing some steps, but by far the best was the dell laptop, witch I found strange.

Is there something with modern computers that makes them not work with Mach3 / LinuxCNC?

It looks like I am going to be forced to go USB or Ethernet.