basically what Regulith said, except if you downloaded your blockland folder somewhere else, dont go to program files ^.^
I installed MINE at: C:/Documents and Settings/Michael/Destop/Blockland
Once again that is where I downloaded MINE personally.. so you download addons into your addons folder WHICH IS IN you BLOCKLAND FOLDER
Hope this helped at all O_O.
PS: Michael in the example i showed you is my personal name.