Spoiler Alert, click show to read:The Others are in a Dharma Project base on one of the small islands that surround the main one. They got there via undersea tunnels.
When the Losties crashed they were living on the East side of the island, hence how Ethan and the other guy were able to get to the crash sites so quick (possibly by tunnels?). They then moved to two camps, one at 'The Door' station (where Sayid goes on the boat) and the new island (a Dharma test facility, note: not a station, theres only 6 of those). The guy Locke etc saw on CCTV is in the Flame Station, the only one the losties havent found yet.
IIRC the location of the island was revealed on a map posted on the Dharma Initiative website, the first pic looks closest to where i remember it.
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