Thank you to all the people that responded. I found a php.spec file for EL3 and modified the php.spec file that came with the php source rpm from the CentOS mirros. Built and installed the php-snmp rpm and it is working great!!! For anyone that would like to have a copy for themselves can find it at http://traffic.wonderwave.net I will leave it up for a week or two so act fast. I also posted the the original spec file, the one with snmp support and a diff file showing the difference between the two. Thanks again to all you helped me out.
Dan