your dhcpd.conf file should hold an example of this
you also find examples in man dhcpd.conf (also found at http://www.8ung.at/spblinux/doc/dhcpd.conf.html
looking into the website of your dhcp server
/usr/share/doc holds a lot of info aswell
for dhcp3 server you can look into
/usr/share/doc/dhcp3-server/examples (this was the first result of searching dhcpd.conf on http://www.google.com/linux
if all of that should fail, i'll post you an example...
don't get me wrong - this place is to be helpt at: these though are the basic steps wich can be used with nearly any trouble in any program...