Does Ensnaring Bridge prevent creatures with zero power from attacking?

Ensnaring Bridge reads: 'Creatures with power greater than the number of cards in your hand can't attack.' A creature with power 0 can only be prevented from attacking if the controller has fewer than 0 cards in hand — which is impossible. Even with zero cards in hand, 0 is not greater than 0, so the restriction never applies to 0-power creatures.

The comparison used is strictly 'greater than' (CR 700.2 covers comparisons, and the card's own text governs). Since 0 is never greater than 0, a zero-power creature is always free to attack regardless of hand size, even an empty hand.

Note that if a creature's power is somehow reduced to 0 after being declared as an attacker, it was already legally declared. Ensnaring Bridge checks at the point of declaration (CR 508.1f checks attacking restrictions as attackers are chosen).

Example: You control a 0/1 Trilobite token and have zero cards in hand. Ensnaring Bridge is on the battlefield. You may still declare the Trilobite as an attacker, because its power (0) is not greater than the number of cards in your hand (0).