Darren McFadden doesn't put the Dallas Cowboys over the top in 2008. Our Achillies Heel this past season was the play of our backup Corner and down the stretch, a lack of depth at Wide Receiver.
Furthermore, we don't need two Pro Bowl players at the Running Back position, which is probably the situation you are looking at if we indeed were to go forward with a deal of this magnitude. Marion Barber III, coupled with a solid change-of-pace Running Back, who adds some speed and big play capabilities would be sufficient. To add, the 2008 Draft by all accounts is an extremely deep draft with regards to Running Backs.
I have to disagree with those that opine that this would not be analogous to the Joey Galloway Trade. Personally, I believe both deals would be very similar. Yes, you would be getting a player valued as the #1 overall pick in return, but could you not say the same thing for Joey Galloway when we acquired him? He was in the prime of his career and there was certainly noone in the previous or that year's upcoming draft that was better than him.