You need build miniupnp first.
Read file "build-unix.txt" in namecoin source dir
for namecoin build requirements.
root@nmcpc:/usr/local/miniupnpd-1.5.20110528# make -f Makefile.linux install
cc -Wall -Os -D_GNU_SOURCE -fno-strict-aliasing -Wstrict-prototypes -c -o netfilter/iptcrdr.o netfilter/iptcrdr.c
netfilter/iptcrdr.c:17:22: fatal error: iptables.h: No such file or directory
compilation terminated.
make: *** [netfilter/iptcrdr.o] Error 1
root@nmcpc:/usr/local/miniupnpd-1.5.20110528#
Take a walk and have some coffee. Namecoin is worth the effort.
I'll help by offering 1 BTC to the first person to write a complete Namecoin installation guide.