Commutators are found on DC motors, not AC (although you could include the "universal" AC/DC types as are found in some appliances).
You can reverse the direction of rotation of such a motor by swapping the connections to the armature (i.e. those connections which go via the commutator) while leaving the field connections unchanged, or vice versa.
If it's a small permanent-magnet motor (which has no field coil) then just reversing the connections of the DC supply will suffice.
[This message has been edited by pauluk (edited 07-06-2004).]