would a smaller smog pump pulley speed up my smog pump or slow it down ... this is on a serpentine system.

Think about it - which would give a longer path for the belt to go around? Same belt speed, longer route, equals slower rotation.

Ok so it will speed it up then ... Will this help lower emmisions by pumping more air into my cat? or won't it make a difference. I found a smaller diameter pulley that bolts right up which is why I am asking. I figure more air int the cat and exhaust manifolds would help burn unburnt fuel.

If your looking to decrease ppm by changing the pulley and introducing more air, I think your going about it the wrong way. The line going to the cat is small, and the lines going into the manifolds are even smaller. Your not going to be able to flow an amount to make any kind of difference. You may increase the pressure, but pressure and flow are two different things. All your going to do is increase the rpm on the pump creating premature failure... and yes smog pumps will lock up.

To give you an idea. I ran my RS on a two speed idle test. Then I pulled all of the smog lines and pump off and ran it again. It passed both times. I cant remember the difference in the readings but they were so minimal that there not even worth mentioning.

This sounds like a BAD IDEA.