Unless, there is another "seer" on the island besides Desmond.
Yes, there is -- cereberus (aka the monster). But it is a different kind of seer, he scans your past!

I think indeed see you in a week means that Ben is coming in -- he has been since the beggining putting Locke and Jack against each other -- playing them both. He is dividing the camp, how Juliet fits on this I dunno. Locke is not with the Others but trust me, Ben will lay his hand and send him back with the belief that Juliet and Jack are traitors...... ok maybe not, but there is something to be said for divide and conquer.....
Ben: "don't hate the playa, hate the game."