Can a creature with 0 power attack?
Yes, creatures with a power of 0 can attack.  Otherwise, it would be very hard to use creatures like Signal Pest which buff your team when they attack, but don't have any power of their own. 

The rules just say that a creature attacks.  There's no stipulation based on power:


  506.2. During the combat phase, the active player is the attacking player; creatures that player controls may attack. During the combat phase of a two-player game, the nonactive player is the defending player; that player and planeswalkers he or she controls may be attacked.