sudo apt-get update
sudo apt-get install virtualbox-ose

If you need usb support in your virtualbox install (great for hooking up devices that are not compatible with linux), you need to install the proprietary version (also free), and do a few tweaks in order to get it to work.

Installing USB Version:

Make sure the open source version of virtualbox is uninstalled:

sudo apt-get remove virtualbox-ose

First, add the respective line to your /etc/apt/sources.list file according to the current version you are running (for example, add the first line if you are running Jaunty):

deb http://download.virtualbox.org/virtualbox/debian karmic non-free
deb http://download.virtualbox.org/virtualbox/debian jaunty non-free
deb http://download.virtualbox.org/virtualbox/debian intrepid non-free
deb http://download.virtualbox.org/virtualbox/debian hardy non-free
deb http://download.virtualbox.org/virtualbox/debian gutsy non-free
deb http://download.virtualbox.org/virtualbox/debian dapper non-free

Download and add the key for the new repositories:
wget -q http://download.virtualbox.org/virtualbox/debian/sun_vbox.asc -O- | sudo apt-key add -

Install virtualbox:

sudo apt-get update
sudo apt-get install virtualbox-3.0

Configure usb support:

Edit:

Editting /etc/init.d/mountdevsubfs.sh is no longer required after further review.

Make sure you are part of the vboxusers group:

sudo usermod -G vboxusers -a `whoami`

Then, logout and back in.

After that, in virtualbox, click on settings for the virtual machine, and go to usb. Make sure enable usb controller is enabled. Then click on OK, and see if it works.

Make sure that you enable guest additions (if it is available for your guest operating system).  It makes the experience a lot more seamless, and easy to use.  You can move your mouse in and out of the guest window seamlessly, and the mouse is then a lot less jerky.

Virtualbox Screenshot

Adapted from:  https://help.ubuntu.com/community/VirtualBox/USB