Virtualization with Virtual Box in Ubuntu

I copied some material from these links in doing this (there are one or two errors in them that I correct here):
http://www.ubuntu-unleashed.com/2008/04/howto-install-virtualbox-in-hardy-heron.html
http://www.linuxhaxor.net/2008/05/05/creating-seamless-virtual-machine-with-virtualbox-16/

1. make sure you have the 'build-essential' package installed:
   sudo apt-get install build-essential
   
2. Download your version of virtual box (probably i386 unless you have a 64 bit processor) and install it
   
   After download, right click the package and install with the GDeb package manager


3. Add your user to the vboxusers group:
   sudo adduser $USER vboxusers


4. Follow the Setup VirtualBox USB Support section here for USB support
   I did both of the things recommended. Note that the last step should read:
   sudo /etc/init.d/mountkernfs.sh start


5. Install Guest Addons and turn on seamless mode
   after firing up the virtual OS, go to the 'Devices' window on the top and 'Install Guest Additions'
   
6. Set up shared directories following this.