I recommend switching to the
new thread.
But like I said before. Viper is like Drow or Sniper. He will punish you if you refuse to return the favour every time he harasses you. All these guys have very similar traits in that they have barely any defense of their own and are slow moving. Furthermore, their autoattacks are actually kinda garbage early on, with Viper being such that his orb actually has a cooldown until level 3. So he can only use that poison on you once every three seconds, whereas you can punch him in the face nonstop. His pathetic normal autoattack won't even graze you.
So the key is to harass them back every time they harass you. It's not easy, but if you do it well you can win every trade simply because you do more damage and you have more health + armour. For example, Spirit Breaker has almost double Viper's effective HP and damage at level 1. You just have to be a bit more manly in the lane and punch him in the face.
Also, remember Viper has another cute feature in that he has no form of burst damage to speak of. What this means is that the amount of damage you take in harass is all the damage he can output. So if you're playing someone like Timbersaw or Slardar, it's quite easy to nuke the living crap out of him after you guys trade harass until half HP. He can't do the same to you.
You should also buy a stout shield if you know you'll be laning against Viper if you're melee.