When can i join the blade of the darkmoons??

Any1 please so and how... i know its at the bottom of the spiralling thing in anor londo but just don't have a clue on what to do!

Also (off topic), will i get invaded by the forest hunters in Darkroot gardens if i have defeated Sif and are hollow?

Darkmoon Seance Ring, after that prompted on the rug. I imagine so for Sif, honestly though I don't PvP or hang around the forest much. You can't be invaded period while hollow, however Gravelords can still curse you.

Elaborating on what whknight said, the darkmoon seance ring is in the catycombs. (thats probably spelled wrong btw) after the second bonfire behind the illusery wall (also spelled wrong) there is aroom with a brick wall that appears to be falling apart. Break that, then run all the way down till you get to a slightly opened coffin. The ring is in there. Then, go to the place at the bottom of the elavator with the ring equipted. The statue will be gone. DONT GO THROUGH THE FOG WALL. Gwyndolin will talk to you. Kneel on the carpet and enter the covenent.