I just received the following from one of my sources. Again it's from a 3rd party and not direct from my source so I'm placing it in rumours for now as I've had no confirmation.
The new arrivals already know most of the facts about the island – and a lot of the why. We won’t find out how they know at first but they’ll arrive and immediately get to work while keeping the Losties busy. Hurley gets caught when he spies on them. Ben is forced to tell the Losties a lot of the secrets of the island. The Losties’ first agenda is to survive – but Ben wants to “save the island”. The Losties will separate when they finally agree with Ben. There will be a lot of fighting – the new arrivals have technology which Ben and the Losties don’t have access to which helps them track their movements. The Losties need to use certain stations and underground tunnels to evade them. The battle will come down to the island’s forces against modern technology.
Source: Bullman