They've shut down the site and it was up as of 10/16/2006.
Go there and you'll see a few more links that give more details. Apparently the threat was more than just a casual mention of the possiblity (which was what I ddid), but was a detailed explanation and a real threat to do it. Here's just a little:
"The death toll will approach 100,000 from the initial blasts and countless other fatalities will later occur as result from radioactive fallout," according to a copy of the posting that was obtained by The Associated Press. The bombs, according to the posting, would be delivered to the stadiums in trucks. All but one of the stadiums -- Atlanta -- are open-air arenas, the posting noted, adding: "Due to the open air, the radiological fallout will destroy those not killed in the initial explosion." Explosions would be nearly simultaneous, the posting said, with the cities specifically chosen in different time zones. The posting said that al-Qaida would automatically be blamed for the attacks and predicted, "Later, through al-Jazeera, Osama bin Laden will issue a video message claiming responsibility for what he dubbed 'America's Hiroshima."'