My 2 cents...that's a great monitor size for a MAME cab. As mentioned, you can either get an ArcadeVGA card, or install the CRT Emu Driver custom ATI drivers (you'll need to use an ATI card) and use GroovyMAME. You'll need to run Windows at 640x480i. Horizontal games will look terrific on that thing. One thing to keep in mind with a CGA only monitor is that you'll have to compromise on the vertical games a bit. Most of them will display fine, but the 280 and above line games (Galaga, Pacman for example) will have to be adjusted so that the top and bottom slightly cut off a bit. If you try and make them fit, then the horizontal games will have a bit of space on the top and bottom, so you have to figure out a good compromise between the two.
If you want to run everything in native resolutions try to find a digital multisync
The other option is to have a rotating CGA monitor (or a separate vertical and horizontal cab) in which case you get perfect resolutions on 99.9% of arcade games.

EDIT:
Just noticed that this monitor also does EGA (512x384 roughly) although I think you may need to manually switch it to use that resolution. Maybe worth asking the seller about that. That would let you run games like 720, Super Sprint and Paperboy at their native res.