It is time to upgrade virtualbox. Normally it is a simple task with simple steps but we have to do them in this order.
In the command line:
Adding the debian repository key to our machine:
user@machine:~$ wget -q http://download.virtualbox.org/virtualbox/debian/sun_vbox.asc -O- | sudo apt-key add -
user@machine:~$ sudo apt-get install virtualbox-3.0
The Sun VirtualBox item in the Applications, System Tools menu will appear in the next bootup.
Alternatively, you can use the Synaptic Package Manager in the System, Administration menu.
By the way, DJ Soul Rebel asked me to post an entry on how to install BT4 directly in a netbook with no virtual machine involved. I will look into that (as you see, there is no deadline committed ;-)