Multipede is an affordable arcade upgrade kit that will add several new features to your original Atari Millipede machine. This kit was originally created by Braze Technologies.
What the Multipede does is upgrades your Millipede game to be a multi-game that also includes the original Centipede (press both start buttons at the same time to change titles). It also expands the high score save function greatly. In addition to those two obvious upgrades, it also adds a setup menu that allows you to alter the dip switch settings without opening up the game.
The reason this kit is possible is because Centipede and Millipede ran on almost identical hardware. The main difference between the two was that Centipede had a 16 color palette, and Millipede had a 256 color palette. A little code hacking on video part of the Centipede game code allowed it to run on Millipede hardware, and from there it was simple to devise a way to put both games on one board.
The Multipede kit works by replacing two key components on your original Millipede game board. The original 6502 processor is removed, and a daughter card with extra components is put in its place. Your old CPU goes onto the daughter card, or you might as well use a new 6502, as they are very cheap anyway. Then a second daughter card is plugged into the sockets that previously contained the 5P and 5R character set EPROMs. Thats all there is too it. If you capable of upgrading a standard PC processor, then you should be able to install this kit. You can also remove the old game code EPROMs, but there is really no need to do so (the game no longer uses them, but if you take them out, then you will probably end up losing them or something).
Multipede kits usually run less than $100 USD and are available from several online vendors. Search google to find them. This is an especially good kit, because it is only a fraction of the cost of buying a Centipede boardset to play in your Millipede cabinet.
Other similar multi-game kits include the Tempest Multigame, Williams Multigame, Multi Pac and Double Donkey Kong.