Are the official plugins still available for download? If so, from where...?

The store is back up, follow the links from Elderscrolls.com in the download section. Link: https://orders.gamesas.com/dlc/

They don't work with the Steam version, though.

Thank you for the link, and the Steam tidbit too...

Wow... I had completely given up hope of seeing the store back online.

Heres the thing though. Does anyone remember how the old installers, if you bought the plugins through the online store, did not work under a 64bit xp or vista and beyond environment? Can anyone confirm that this is still the case, or do the plugins work properly now?

Battlehorn Castle works with Win 7 64bit, at least.