The VisionRGB cards are particularly suited to 15KHz capture, which is officially below the VGA standard (IBM VGA is 31KHz). As Qlex mentioned the StarTech PEXHDCAP (which is a no-name version of the Micomsoft SC-500N1) is also capable of 15KHz capture at a much lower price point, albeit with lower picture quality (see here to compare the quality, top and bottom left is VisionRGB, top right is PEXHDCAP). You're right that there's a difference between JAMMA and VGA, most notably the RGB signal level is 3-5 volts peak-to-peak, whereas VGA is 0.7 volts. Of lesser concern is that VGA officially dictates separated horizontal and vertical sync, but the very common practice of using composite sync on the horizontal sync pin of the VGA connector is supported by practically all monitors and capture devices. In order to bring down the levels, the most easy method is with a serial resistor, I use 220Ω but as I recall Burbruee was having problems with the picture being too bright so he used a higher value. Keep in mind that only the RGB signal lines should be reduced, sync should stay 3-5Vpp (so passed through untouched from JAMMA) because it is considered a digital TTL signal.