Well, you may want to consider several options.
1) There are VGA to TV converter, and VGA to S-Video converters. These are good for using TVs. S-Video will generally result in a bit clearer picture with better color depth than standard composite video. I would advice against using an RF Out (i.e. Channel 3 or 4).
2) You may want to go buy a video card with TV Out. This may be a good option, because the TV Out is generally better than running through a converter (as above).
3) You may want to consder a PC Monitor in your Cab. PC Monitors aren't as authentic look, but are easy to use. I heard the Hansol series looks good for Games. Wells Gardner also makes some "Arcade Like" VGA/SVGA monitors that work well. However, installation of any monitor can be dangerous (if it is NOT incased). With a VGA/SVGA monitor, you will have the luxury and safety of running windows.
4) If you are experienced and serious, and just want to run MAME only, and really want the "arcade look", an Arcade monitor may be for you. Arcade monitors look like the real thing. However, there are some serious limitations to consider. Most arcade monitors run at 15Khz and are difficult to handle, and dangerous inside. You MUST use advanceMAME, and it is generally NOT safe to run windows (although it can be done under certain circumstances). If you conisder this option, I recommend a J-Pac.