I recommend that rather than downloading and installing the .deb file, you follow the instructions on the Linux download page to add the VB repositories to /etc/apt/sources.list. Then copy that long command to install the repository key by pasting it into a terminal.
Once you done both those things, just run
If you follow these steps, VB will be managed like all the other packages on your system. You will be notified if updates are available which you can install using the System Update function that you use to upgrade all other packages on the system.
sudo apt-get update
sudo apt-get install virtualbox-4.1