Prevent Defense

Can somebody please explain something to me? How does this Obama/Gates troop build-up, over in Afghanistan, significantly differ from the one that Nixon/Kissinger implemented (Melvin Laird actually pushed for troop reductions) back in '69, during Vietnam? I mean, I know that they're different countries with different topographies and all, the Taliban having had the temerity to harbor Al Qaeda, etc.. But now, as we speak, I'm saying, how are they at all different? Educate me, please.