Got this from the Vikings website...
Moe Williams: The Vikings started last year 6-0 while using Williams as their starter, so he's got the confidence of the coaching staff. Even if Onterrio Smith is available, Williams will see plenty of action. But against a very solid Dallas run defense, I don't see many yards coming Williams' way. His best chance of being a fantasy factor is at the goal line, or perhaps as the recipient of a touchdown pass—an area where Dallas' defense struggled somewhat last year.
Onterrio Smith: Smith may be available to play in this game, and if so, he'll likely see nearly as much work as Williams. But even so, maintain modest expectations for Smith. Dallas allowed just five rushing touchdowns last year, by far the fewest in the league. With a score unlikely, and with Williams getting carries too, your best hope is to get 50-75 total yards from Smith.