There is a problem installing nmap using the apt-get package installer on Ubuntu 12.04. The problem appears to be with the sub-build of ncat, so you can build the package without it.
But if you need ncat (as I did) you will need to edit the LUA_LIBS definition as part of the make.
First install the package prerequisites:
sudo apt-get install checkinstall build-essential
Now download the package tar bundle
Extract the tar bundle
tar -jxvf nmap-6.40.tar.bz2
Now configure and make the package
cd nmap-6.40 ./configure make "LUA_LIBS=../liblua/liblua.a -ldl -lm"
Run checkinstall and accept all of the defaults
sudo checkinstall sudo dpkg -i nmap_6.40-1_amd64.deb
You can test the package is working by running the following command
nmap -A scanme.nmap.org