We are converting an old oxy-acetylene flame cutting machine to CNC, this is our 1st attempt at something like this. We're using a PICO Systems Universal Stepper Controller as our control board.
    The machine has 3 120v electro magnets that open the valves to allow the gases to flow to the torch. Can anyone help us with how to use SSRs to operate these?

This is the way I would do it.

Use SSR's similar to the one in the picture - they have opto isolation on the input and can be driven by either 3.3V or 5V logic from your parallel port. The output pins you choose should be configured 'Active Low' within Mach.

Tweakie.

Thanks Tweakie, I've just ordered 3 of them.

Those are a bit overkill.
There is a neater more compact way with boards made by Opto22 or Crouzet P&B among others.
They include indicator lights and fusing.
e.g. Ebay    170540341208
N.