You can download Virtual Box from http://www.virtualbox.org/wiki/Linux_Downloads
You can download a package specific to your distribution or use the generic package. In My Fedora 11 installation, the RPM package cannot be installed. So, I decided to use the generic package.
Assume that the downloaded file name is:
Basically, just open a console, go to the directory where you saved the file and execute:
chmod a+x VirtualBox-3.2.6-63112-Linux_x86.run
It should be installed automatically in /opt/VirtualBox.[/code]