This is a lengthy topic !

Quick question ? There's certainly no quick answer.
Have a go researching through the sticky posts, searching for relevant past posts, referencing the BYOAC Wiki pages, and consider purchasing Saint's book :
http://www.amazon.com/Project-Arcade-Build-Your-Machine/dp/0764556169/ref=sr_1_1?ie=UTF8&s=books&qid=1212125903&sr=8-1Where to start ?

I'm a novice compared to the old-timers on this forum, but for what it's worth ...
You'll need to add a computer with Mame installed (naturally).
To interface the current controls and monitor to your PC, using the arcade machine's JAMMA interface :
>> You'll need a J-PAC interface :
>>
http://www.ultimarc.com/jpac.html>> You may also need an ArcadeVGA card, depending on the capabilities of your current video card :
>>
http://www.ultimarc.com/avgainf.htmlThe JAMMA interface only provides Mono sound capabilities, so you'll probably want to add some stereo speakers, that are hooked up directly to the PC.
You may wish to add further controls, such as a spinner and trackball, but you can deal with that down the track.
If you decide against using the JAMMA interface, then you'll need to purchase an encoder such as I-PAC or KeyWiz, and rewire your controls to the new encoder. You'll also need to address the monitor issues described above (ArcadeVGA card), or alternatively, replace your Arcade monitor with a PC monitor.