The commented suggestion works. Install network-manager-openvpn-gnome and its dependencies. If you cannot connect to the internet without the vpn, you will have to get them from Ubuntu's repositories through another computer. Start here http://packages.ubuntu.com/ Then select your version and search for the package by the above name. When I installed it on Lubuntu 12.10, it required 4 other packages. Make sure you download those as well, and install them first. You can install the .deb files from a command line using (trying to run them from a file manager might work as well):
sudo deb -i packagefile.deb
If you can find the dependency order of all of those packages, then install them in an order such that no package is installed before a package that it is dependent on. This will make things much simpler.