Great article on the insurgency in Iraq and why the U$A will loose - same may well apply to Afghanistan;
Fact number one about guerrilla wars: They're not over until the guerrillas win. Mao set out the guerrilla's viewpoint 80 years ago: "The enemy wants to fight a short war, but we simply will not let him." The longer the guerrillas stay in the game, the sicker the occupying army gets. Sooner or later, they'll go home -- because they can. It's that simple, and it works. So anyone who tells you it's over is just plain ignorant. That's one thing you can rule out instantly.