page refers to the original 40 player version of Naxx.
the World of Warcraft: Wrath of the Lich King
was moved to Northrend and retuned to be the introductory level 80
Until we get a Naxx guide up and running you can find some good info
on the Northrend Naxxramas at WoWwiki.
The Killer Guide's Wrath
of the Lich King guide has
some very basic info on the 10 person Naxx, better info on the WotLK
5 person instances, and a lot of good general and class info (including
Death Knights) for Wrath, in addition to Horde and Alliance 60-80 leveling
Naxxramas was indeed in the Eastern Plaguelands, but after Kel'Thuzad's
phylactery was given to the treacherous Father Inigo Montoy, the lich
was able to revive himself and make the transition along with his fortress.
Floating above the Plaguelands, the necropolis known as Naxxramas serves as the seat of one of the Lich King's most powerful officers, the dreaded lich Kel'Thuzad. Horrors of the past and new terrors yet to be unleashed are gathering inside the necropolis as the Lich King's servants prepare their assault. Soon the Scourge will march again...