Thanks guys for all your help!
Unfortunately Visio won't convert text to lines and arcs, so I will have to use one of the text to G code converters. I tried both deskengrave and stickfont, but the only problem with them is they make one line at a time. I am engraving signs for electrical equipment, and the placards require multiple lines (and sometimes up to a small paragraph and a diagram). I am worried about being able to center the text on the piece, keeping multiple lines of text aligned, and then going back to Visio to create lined diagrams.
I guess there is no free software that could help me. Would you recommend AutoCAD or a similar 2D CAD program that can convert its text to lines and arcs? I can place the text and lined diagrams where I want on the plastic, then import the .dxf file into Mach 3 and create the G Code and (hopefully) machine the plastic how I have laid it out.
Thanks again,
Alex