Go to the WotC D&D website and login to D&D Insider (if you have a WotC messageboard account, it's the same as that).
Then click on Dragon at the left side and below that Features, and the first feature is up...
click on Fortress of the Yuan-ti and then prepare to be disappointed....
That's all that's available so far, there should be something else today (but don't hold out too much hope). No idea when Dungeon articles will turn up (although saying that the Dragon article would have better suited Dungeon).
Still at least you aren't being forced to pay for it (yet).