I've been using:

send host-name "foobar";
send dhcp-client-identifier "foobar";

in dhclient.conf, for a host named foobar.domain.com, and then have
set the fixed addresses in dhcpd.conf on various machines based on the
hostname or identifier.

It seems dhclient should have an option to construct a client
identifier from the mac address automatically, but I find this much
less helpful since I don't want the address I get to change just
because I plugged in a different interface.

-- 
        Greg Troxel <gdt@ir.bbn.com>