using mame, you would need a computer/laptop with at least 1ghz. if your going to use a old gaming machine, chances are the screen is no good for mame. most of those old screens won't run pass 300 lines, and vga output is pretty much just rgb output, which you could wire up to any tv/monitor but you would need the hz refresh rate to be up there.
You may have to adjust the sync rate.
http://www.epanorama.net/circuits/vga2tv/composite_adapter.html