In Ubuntu, pip is provided by the python-pip package. You can install it in the Software Center, or, if you prefer to use the command line:
sudo apt-get update && sudo apt-get install python-pip
If you have not already installed python-dev and build-essential, you should install them too. (But it seems your apt-get command might have successfully installed them. If you’re not sure, you can check by trying to install them again. Or with apt-cache policy python-dev build-essential.)
Once the necessary software is installed, if you wish to update it further, you can do so with pip itself, by running:
sudo pip install --upgrade pip
sudo pip install --upgrade virtualenv
