If your cabinet is indeed a JAMMA Cabinet, you can buy a J-Pac and the ArcadeVGA video card from Ultimarc.com.
JAMMA is a type of connector that most PCBs attach to, with a standard pinout. The J-Pac allows a PC to connect to this connector in your jab, allowing video to be sent to the arcade cabinet monitor, controls to work, and more. The J-Pac also connects to your PCs video, and keyboard or USB ports for key in, and has ability to wire for sound as well.
The ArcadeVGA video card allows your PC to output at the arcade monitors lower resolution and refresh rate. Most arcade monitors use 15Khz mode, where PC monitors use between 31 and 48Khz. There are other cards that output at 15Khz, but you will need to configure AdvanceMAME. The ArcadeVGA card makes configuration a snap, because its BIOS is designed to run at 15KHZ almost all the time.