I'll bite and say Man United will win this weekend. They looked like a cohesive unit in their preseason friendlies and they're certainly ready to start the season. 2-1.
I reckon Man Utd will be very tired from their US tour and the game in Portugal, which could give us the edge. The French players (Pires, Henry and Wiltord and Vieira) will also be fresh as they haven't played a full pre-season. This on top of the fact that United have sold two top-class midfielders and failed to replace them.
2-1 Arsenal win. I am also going to make a few guesses here. Wiltord and Henry with the goals in that order. The Man U goal comes from Ruud. Howard is in goal for the whole game but still wins the starting position.