I hope you know that Taliban won't accept a man made constitution! Mullah Omar only said he's open for talks! Don't jump to conclusion that he is ready to accept all the terms your offering (even the ones that go against Taliban)!
This isn't anything new, NATO, America and Taliban had talks before and nothing came out of it!
And secondly, lets not forget what happened to the Soviets after they negotiated with the Mujahideens and tried to save their face by withdrawing from Afghanistan! The Mujahideen overran Kabul and the Afghan Communist Gov of that time!
So what makes you think that Taliban, in a time when they have the upper hand and the momentum, would want to negotiate?
Maybe in the dreams of the NATO and Americans, but the reality tells a different story!
Afghan's won't negotiate for any peace, its in their nature that they don't bow to invaders! 30,000 extra troops will only give more support to Taliban!
I guess you people haven't learned from the mistakes of the Soviets!