It has already been mentioned, but I am going to reemphasize the point.
Barack Obama will not get impeached because he was acting entirely within the War Powers Act of 1973. He notified Congress of his actions, and sixty days have not yet passed. If soldiers are still committed to the action in Libya after sixty days (which Obama has already stated will not be the case) and Congress has not approved the action, then someone might have grounds for impeachment. As it is, Obama has done nothing wrong.
As Nitramj pointed out, Bush started his actions in the Middle East without congressional approval. As we all already know, he would receive the approval for it. Thus, Bush, like Obama, did not perform an unconstitutional action either.