Animate Artifact

Enchant Non-Creature Artifact    (CMC:4)

Enchant artifact 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.

38 ME4 • ENDouglas Shuler

™ & © 1993—2011 Wizards of the Coast

Legal in: Legacy,Vintage,Commander

Oracle Text (click to copy):

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 his or her most recent turn. It doesn't matter how long the permanent has been a creature.