If you are a competitor of Astana, here are the goods:
In the tour there are these big "hump like" structures on certain stages called mountains, and the only descent riders from astana that can really take on the climbs is Lance Armstrong and AC. If you watched the Giro tough, Lance showed in the late stages weakness in the climbs. Levi in the Giro was worse than Lance in the climbs, and I don't figure Levi to be a great climber. So just from going by Lance's and Levi's weakness in the Giro on the climbs, the best time to attack Astana would be during the mountain stages and try to isolate AC. I love Lance but I feel that he could get dropped in the mountains, though it would be nice to see him dominate.
Once AC is isolated it's going to take a combined effort from the other teams with GC contenders. I think the other teams need to literally gang up on Astana during the mountain stages. It needs to be a planned, organized and coordinated attack though on a particular mountain stage. Not sure if other teams would be willing to open the line of communications before the mountain stages, share tactics, however, and agree to a combined effort to attack Astana. And I'm not sure if that is even allowed in the TDF as well.
I'm thinking if Rabobank's Menchov, CSC's schleck, Garmin's man, etc. need to combine forces to get their GC men back on top.