Networking :: Restrict DHCP Assignment To List Of Macs

I have a lab with 1 switch and 2 machines attached. One XP station and a debian lenny server. My debian runs dhcpd with this configuration:
subnet 192.168.1.0 netmask 255.255.255.0 {
range 192.168.1.31 192.168.1.254;
default-lease-time 345600;
max-lease-time 691200;
option routers 192.168.1.1;
option subnet-mask 255.255.255.0;
option domain-name "lab.com";
option domain-name-servers 192.168.1.12;
option netbios-name-servers 192.168.1.12;
option netbios-node-type 8;
option broadcast-address 192.168.1.255;
option ntp-servers 192.168.1.12;
ddns-updates on;
ddns-update-style interim;
}

I'm trying to restrict dhcp to only provide setting for a list of MAC addresses (about 300 macs)
Using the following option is not good to me because I have not a pattern in my clients mac.

class "private-hosts" {
match if substring (option hardware,1,11) = "01:00:50:56";
}
pool {
range 192.168.1.31 192.168.1.254;
allow members of "private-hosts";
}

I've try using iptables with following configuration, but XP still getting IP from dhcpd:
iptables -P INPUT DROP
iptables -P FORWARD ACCEPT
iptables -P OUTPUT ACCEPT
# Full from Localhost to Localhost
iptables -A INPUT -i lo -j ACCEPT
# Full from My PC
iptables -A INPUT -s 192.168.1.2 -j ACCEPT
So I can't limit DHCP for specific macs.