VirtualBox 4.0.6 is launched and available for Ubuntu 11.04 Natty Narwhal, VirtualBox is an virtualization application which originally created by innotek GmbH, purchased by Sun Microsystems, and now developed by Oracle Corporation as part of its family of virtualization products. using VirtualBox we can teste the Operating system without installed it 'regularly' in our mechines. VirtualBox is available for Ubuntu 11.04 Natty Narwhal and it's previous version, you can install the new VirtualBox 4.0.6 via apt-get install through following command :

Add the Software Source 
Add VirtualBox 4.x software source to your apt database
deb maverick contrib non-free
deb lucid contrib non-free
deb karmic contrib non-free
deb hardy contrib non-free
deb squeeze contrib non-free
deb lenny contrib non-free
Note : Up to version 3.2 the packages were located in the non-free section, starting with version 4.0 are located in the contrib section.
Update and Install
Now ready to install VirtualBox 4.0.6 on your system.
sudo apt-get update
sudo apt-get install virtualbox-4.0
More Information
VirtualBox needs extra configuration in order works with USB, a tutorial 'How to get VirtualBox work with USB' can be found at