I think you are talking about the bios chip that you can install in the NEO AES system.
I'm looking into getting one of these since I don't like green blood on Samurai Shodown II. I think massystems.com does it (FAKK2 told me). I think I will head over there since its 15mins from my house.
I know most places sell them online for about 15-20 bucks (the mod chip).
You can play imports on the AES system but I don' tthink you will get blood or bouncy boobs or anything....
I thought i saw this mod at GamesX once but when I looked again I couldn't find it. What you're looking for is the reigon mod. It's very similar to the Saturn reigon mod in that you're just changing a few jumpers.
I seem to recall the board with the jumpers you need to short was tan colored and it might have even had USA and JPN labels near it. I don't have an AES system to check though. Sorry.
so wait, the system was set up in such a way that the if you play an import game on it it's the same basic game but it's encoded to somehow sensor it depending on what regoin it's from? That's pretty clever...
all home aes carts are exactly the same chips as the arcade systems mvs carts (Riding Hero and Magician Lord being the exceptions thier P roms are different if I remember correctly)and the boards are shaped different and the home cart uses less pins, the mod chip or aka the bios chip is sold and installed by MAS SYSTEMS, with it you can set different options hidden within the game you only should be able to access it only if they (the rom chips) are in an mvs cart and in an mvs system, you can then press the options button and the menu will display. the BIOS chip enables the AES system to do the same thing as the MVS system. its nice to have. and even if you dont have the bios chip you can allways play japan or european carts on the home aes system but the bios in your neo-geo system decides what roms to read on the cart, giving you the censored blood and non-bouncyness in games, but....with the new bios you tell it what you want, blood on or off....credits 3 or 8 , men 3 or?, etc..etc... and then you reboot, and your game starts the way you set it up.
you can do the same thing with the Arcade MVS-AES converter playing MVS carts on the home unit.
I also was screwing around with the neo geo unit as I was bored when I was younger, and I found out you can set your unit to japan mode without any mods at all, but you risk damaging the system everytime you do it, I took off the cover and looked at the board and put in a cart, turned it on and watched it boot up, as it boots up I would take a metal screwdriver and run it down the right side of the big SNK chip, you know, there are 3 of them in the system with tons of little pins coming out, I ran the screwdriver down the right side of the middle chip (very, very, very lightlynear the top half of the chip) and it sparks a tiny bit and scrambles the unit for a second, results were, MVS sometimes, and sometime JAP mode.
it worked for about 4 years, then I was messing with another side of the chips and screwed my system up, it looked glitchy, but SNK said 75 bucks and get a new system. so I did that and stuck with the 1 little area.....I also messed with the sound chips and found one of them when screwed with gives you tons of sound effects from the game, voices, punches...etc... like neo jukebox....and one spot paused the game permanently in case you get to a spot in a game you want to listen to the music (like the endings of Crossed Swords or Blues Journey for example) you short out that spot and the screen would freeze and the music would still play.