I have a macbook 13.3 in white. I want to install snow leopard on it.

I have a macbook 13.3 in white. I want to install snow leopard on it as it meets the specifications. When i insert the disc, it says that snow leopard can not be installed on this macbook. what might i need to do? also i noticed that when i go to ABOUT THIS MAC, it will not show me the serial number. Instead it just reads serial number: system serial number.