*bashes head against nearest brick wall*
I have now and it's all good! Apologies for the stupid question.
And now for another....
Is there an obvious way to start a VM at boot time? I've told the virtualbox interface in the unRAID web interface (not phpVirtualBox) to do so, but the console just gives a message saying "nothing in list" when I boot the physical.
The reason I'd like to get it working is because the virtual's providing local domain DNS, a mail server and (most importantly ) an iTunes instance so apple HomeShare works