As long as enchanted artifact isn't a creature, it's an artifact creature with power and toughness each equal to its converted mana cost.
8/1/2008 This card has been returned to its original functionality. If it is enchanting an artifact that’s already a creature, it won’t change its power and toughness.
8/1/2008 A noncreature permanent that turns into a creature can attack, and its abilities can be activated, only if its controller has continuously controlled that permanent since the beginning of their most recent turn. It doesn’t matter how long the permanent has been a creature.