Yancek is correct. You are using an unsupported version, and will not be receiving important updates, including security patches. I'm sure everyone will agree that you should upgrade. Download a new iso of the newest version of Ubuntu or a different distro and install from that.
You seem to be a little confused in regards to package managers. Most package managers on linux distros these days are rpm (rpm package manager) or dpkg (debian package). rpm will install ".rpm" packages with the command "rpm -i foo.rpm" and dpkg will install ".deb" packages with the command "dpkg -i foo.deb". Typically a distro will only have one of these package managers installed; Ubuntu comes with dpkg, not rpm; so you need to locate a .deb file, not a .rpm.
Further more most distros do not just provide you one of these package managers, but also an automated tool, as well as a repository of packages; to help you with managing packages. These tools work with the package manager and make installing packages extremely easy.
Ubuntus automated tool is called apt (automated package tool), and installing a package is as simple as opening your terminal and:
sudo apt-get install netcat
There is no need to locate the .deb file, as apt-get will go out a fetch it from the repositories, plus any other packages needed to make it work, and install them all for you.
It's that simple. I hope that's helped, but most important is that you upgrade that version of Ubuntu. You should do this and then install netcat, with the command i gave you.