Assuming you are using Linux Mint 14, which is based on Ubuntu 12.10 aka quantal, then the problem is this package is not included any longer in the repositories. It is obsoleted and replaced by pyhton-qt4. If what you are trying to install doesn't have a more modern version, and you have no suitable alternatives, you could try downloading the .deb file from an older Ubuntu repository. You can find it here: http://packages.ubuntu.com/search?keywords=python-qt3
. Download the .deb file for your architecture and double-click it in your file manager to try and install it. You will probably get errors that it has more dependencies that can't be satisfied. Download and install those the same way, before trying again.