The way that wars against foreign invasions by great powers are won, robomatic, is by eventually making the foreign troops leave. You do that by making the cost of the occupation too high. Yes, the former Viet Cong could indeed offer some useful insights on how to achieve that result.

I do regard the Taliban as having been an absolutely detestable bunch when they were in power, and I have no liking for them whatsoever. I do not regard the Viet Cong in that light, however. I think they were fighting for a worthy and legitimate cause, and they eventually won it.

I know you asked "what will win it?" in regards to Afghanistan. Well, the question is "win it for whom?" isn't it? I wish to see the Afghans win the war. Given that there are a number of different factions among the Afghans...that makes things a bit complicated...but for me that war will be "won" when the foreign occupying troops are driven out of that country in the same manner that the Russians were driven out of in in the late 80's. Whoever among the Afghans then picks up the pieces, I would hope it would not be the religious fanatics in the Taliban again, but that will ultimately be up to the Aghans, not to us, because it's their country, not ours.