Improvised weapons are either close enough to a real weapon to be used as such or does 1d4 damage. Since a two-handed weapon does not resemble a weapon that can be wielded in one hand, at best it does 1d4 damage. If your DM rules that it can be wielded one handed.
Well, some of us think it a two-handed weapon DOES resemble a weapon that can be used in one hand. i.e. a greatsword and a longsword are both swords (it's right there in the name), one is "just" bigger than the other.
If you disagree with that, then rule it an improvised weapon and be done with it. The discussion in this thread doesn't concern you, since it's a just a bunch of wrong-minded people debating imaginary stuff that doesn't matter.
