I do this in /etc/dhcpd.conf:

subnet 209.157.85.48 netmask 255.255.255.240 {
        option routers 209.157.85.49;           # nfs1.clock.org
        option subnet-mask 255.255.255.240;
        option broadcast-address 209.157.85.63;
        option swap-server 209.157.85.49;       # nfs1.clock.org
        option domain-name "clock.org";
        option domain-name-servers 209.157.85.49, 209.157.85.50;

#       host atomic {
# Sun SPARCclassic (multihomed)
#               hardware ethernet 08:00:20:04:d3:67;
#               fixed-address atomic-le1.clock.org;
#       }

        host jittery {
# Macintosh PowerMac 7600/200 MP
#               hardware ethernet 00:05:02:80:39:b3;    # built-in
                hardware ethernet 00:00:94:ad:a9:d5;    # Asante 10/100
                fixed-address jittery.clock.org;
        }

        host inverted {
# Macintosh PowerMac 8500/150
#               hardware ethernet 00:05:02:50:fe:fe;    # built-in
                hardware ethernet 00:00:94:ad:56:84;    # Asante 10/100
                fixed-address inverted.clock.org;
        }

        host biological {
# Purple ("Grape") Apple iMac
                hardware ethernet 00:05:02:49:7d:92;
                fixed-address biological.clock.org;
        }

        host lunar {
# PowerMacintosh G3/400 ("blue moon")
                hardware ethernet 00:50:e4:a0:ac:12;
                fixed-address lunar.clock.org;
        }

        host solar {
# Sun SPARCstation 2
                hardware ethernet 08:00:20:0e:fc:2d;
                fixed-address solar.clock.org;
        }
}