As with the lighted button idea I'm getting a fair amount of e-mail on this so I'm just putting up a quick post on it. Basically I lit my sideart by mounting 12" blue neon car subwoofer rings inside holes on either side of my cabinet.
If you haven't seen my NEON MAME project thread here's what I've done...
My first step was to cut a hole in one side of the cab after determining a location that will be hidden behind the front bezel. I made the hole the same diameter as the inside of the neon ring but if you wanted the ring to be more hidden you could make the hole smaller.
I used a circle cutting jig in my router for this for a perfectly round hole. I then laid the finished cab side onto of the other one and traced the hole onto it so it would be in the exact location on both sides.
I also put t-mold around the inside of the holes for a real polished look. I cut the slots for that at this point as well.
Mounting the rings is really just a matter of screwing them to the inside of the cab. There are standoffs on the ring for screws to go though, there were 4 on mine...
Of course you won't want just a ring in there, you want some sideart to light up. To do that I made a 'sideart sandwich' consisting of: a piece of 1/8"plexi to protect the sideart/the sideart itself/and a wood backer(1/2" MDF).
Unfortunately I didn't take any pics of this part but I think it's self-explanitory...I hope anyway.
Once you've made your sideart sandwich place the neon ring on top of it and drill holes down through the sandwich where the 4 mounting holes are.
Once that's done just screw the whole thing in place on the inside of the cab and wire the inverter to a 12v supply. I used my computer PS as I did with my LED buttons. You can tap the yellow+black wires of an unused molex connector to get 12v.