Try this: [url]http://www.fogproject.org/wiki/index.php/Setting_up_ProxyDHCP[/url]
When you get to step 7, modify line [B]dhcp-range=192.168.1.10,proxy[/B] (almost at the end of the file) to match your DHCP server IP address (dhcp-range=x.x.x.x,proxy).
This is a solution when you cannot -or you don’t want to- modify DHCP options 66 and 67. I have it working this way because options 66 and 67 are already busy.