1. He couldn't have voted, but Obama spoke out publicly against the Iraq incursion in October 2002, before the senate voted. Ergo, he was against the use of force.
2. It's debatable whether the democratization of a mid-east country would ever have worked. History is rife with the US attempting this all over the world, usually with disastrous results. One thing is clear, Saddam Hussein was far from the worst thing that could have happened in Iraq, as we are seeing - and that's on Bush, especially as he fabricated the reasons for deposing him.
3. Obama found the ME in utter chaos, and likely stopped another Vietnam with his actions. If the region is a mess now, that's on the Bush family (see #2, above).