They're awesome. I love millies. The ones you're talking about go by the name African giant black millipede, or variations on that name, usually with some parts of the name missing. Scientific name:
Archispirostreptus gigas. They can get almost a foot long, but don't need a terribly huge cage. A 10 gallon will house one nicely, but a tupperware will work even better and cost less too. Height isn't important cause they don't climb. You can use soil, cypress mulch, orchid bark, Bed-a-beast, and similar substrates. Try and make it deep enough to burrow in (the 'pede, not you
). They really don't like light, so put the cage somewhere where it will stay pretty dark. An opaque tupperware with a lid that will block light will help. You can drill air holes in the top of the lid or in the sides of the tupperware. I prefer the sides cause it doesn't let out as much humidity that way. It's still a good idea to have some hides in the cage. Cut a hole in a Coolwhip container or something and you've got a cheap, yet effective hide.
Put a small dish of water in there, but no dish is necessary for food. They eat dead and rotting plant matter. You can feed them kale, collards, fruits, veggies, all sorts of plant matter. If they don't eat it right away, don't worry. They often like to wait till it starts to rot a little, so if the food starts to spoil, don't throw it out just yet. I'd often feed mine my leftover apple cores and the stems from the collards I feed my turtles. They'll get rid of any nasty peas or lima beans on your dinner plate too
Keep in mind that millipedes are poisoness. They don't have a venomous bite, and rarely bite anyway, but they can ooze poison through pores in their sidesas a secondary defense. It's often a yellowish color, and it stinks bad too. It can really burn the eyes and nose for a while, but its not too bad. Millipedes will rarely do this though, and only if you really provoke them. The degree of poison that they have varies with the species, but the poison isn't really that dangerous, more of a nuisance. You'd have to ingest it, a LOT of it, and even thenm, it wouldn't kill you or anything. If you ever got any on your hand, just wash it off. It will stain clothes sometimes though.
Their primary defense is to coil up. NEVER try to break a millipedes coil, you could actually break the millipede in half before it will relax. When you pick one up, they'll often coil, but just let it sit in your hand and it will soon come back out and start to explore. They have really crappy eyesite, so they use their antennae and feel the ground as they walk, like a blind man's cane almost.
I had a giant black pede several years ago. They're really cool pets, and very low maintinence. Here's a cool site that has caresheets on pet bugs, inlcuding millipedes:
http://petbugs.com/caresheets/
