In reply to Blanka: I can't connect over DVI as the laptop I use only has VGA output. Also the monitor only has VGA anyway.
OK I switched "switchres" off and now the monitor has stopped with the auto setting messages. So that's cool.
I'm using the latest Mame v.132 and am using d3d. However Frogger still displays small (approx. 7" screen size). In fact I would actually like to have all the games displayed in a small area like this as I'm building a scaled down bartop. The 15" monitor is nice but I would like to scale the display to about 9" or 10" size if I can.
I thought about making a black bezel that would be used for all vertical games, and yet still keeping the same 4:3 aspect ratio. I dunno if I'm thinking along the right lines though. Maybe there is an easier way to do what I want just using the mame.ini? Sorry I'm a bit of a n00b and I'm unsure what all the options there actually do.

If I could just work out what makes Frogger display the way it does, then I could tweak that so it displays slightly larger and then apply the same to all vertical games.