He probably means "standard resolution", which is 320x240. Most MAME games will work on a standard monitor natively, though you will need to tweak the settings to get each game to show correctly. For the games that require a higher resolution, you can use hardware stretching to make due. You will also need to do that for games with opposite orientation (monitor mounted horizontal, game designed for vertical).
If you do go with an arcade monitor, you're going to want an ArcadeVGA board from Ultimarc (or buy it directly from Divemaster if in the US).
Figure out what the make, model, and size of the monitor are. Also, if you can have the guy power it up and see what the picture looks like, this is pretty important. (Unless you are comfortable with rebuilding a monitor chasis).