Aaron Plays Dark Souls: Prepare to Die! - The Darkwraith Covenant
To access the Darkwraiths you must get the Lordvessal and NOT talk to Frampt. Actually, I'm not even sure if you need to get the Lordvessal first, but I would imagine you do. Anyway, kill Sif to get the ring of Artorias so you can traverse the Abyss. Head to New Londo Ruins and procure the Key to the Seal from killing the Sealer or having him give it to you (if you have Lordvessal). Drain the Ruinis, dead down, kill the Four Kings, and then Kaathe will appear near the bonfire to talk to you about some different options you could take in regards to Gwyn and the Kiln situation. You don't have to enter the convenant to unlock it, but you do have to bring up the Join Yes/No option.
This video, and others in the series, can be found here:
http://tinyurl.com/cwb33su
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Aaron presently has 60,318 views for Dark Souls across 77 videos, with his channel uploading 5 hours worth of Dark Souls videos. This is 3.64% of the total watchable video on Aaron's YouTube channel.