Disabling DCHP on Small Business Server for wireless

Hello,
I am working on installing a Small Businss Server at our office.  I have a dilema when it comes to the wireless and DHCP.  Our RF guns used in shipping do not support encryption of any kind so we have always had open wireless access points in the building.  This hasn't been an issue as we have never had a DHCP server so if someone tried to get onto our network they haven't been able to get an address to do anything.  Now that we are going to have a SBS though they would get an address, I was thinking of adding an exclusion under filtering in DHCP to exclude Apple Mfg. ID's etc. so that employees who have tried with their cell phones for example would not be able to to get on.  I am wondering if that would work as well as if anyone has any better ideas on how to do this, the wireless access points are Cisco 1200's and I don't see anyway in there to prevent DHCP from "going through them".  
I really appreciate your assistance with this!