OK most of the advice above is pretty solid IME.....one caveat though, as with any kind of envenomation, you want to watch for signs of anaphlaxsis (shock symptoms, extreme swelling, persistant pain, nausea, rash/hives etc). I have been speared a few times here and there and the pain never lasted more than 20-30s so the 30' quoted would concern me a bit. As with other types of stings, I suspect can get sensitized to the venom as well. Probably not a bad idea to consult with a medical professional if the symptoms are severe or persistant.
Teena, There are a few species of urchins like the longspines that sting and some others actually have smaller, pincer-like spines close to the body that are extremely toxic ( ie the fire urchins). These have been implicated in human deaths (shock, as above but much worse like in sea wasps and box jellies) so I don't know why you would want one in your tank.
Some of the other common species still have barbed spines that will stick in like the longspines do (without the venom).