Ok, I have got slightly further with this.
Currently, when booting, my virtual LMCE media director hangs on "[53.846691] e1000: eth0: e1000_watchdog: NIC Link is Up 1000 Mbps Full Duplex, Flow Control: RX" during startup. This happened a number of times from the word go; however, on one occasion, the boot process continued and "setup.sh" ran like normal. However, since restarting, it is now hanging again at the aforementioned part of starting up.
My /etc/network/interfaces currently looks like this:
iface lo inet loopback
...which looks nothing like yours, justnulling! Is all of that extra stuff necessary for this netboot in VBox to work?? I did try using that code (and replacing _USERNAME_ with my username), but "/etc/init.d/networking restart" gave me a funny error, plus I couldn't changed "eth0" to "tap1" in VBox network settings as per your suggestion.
I did, however, change "NAT" to "Host Interface" in the VBox network settings, but that was all I did to make it work (and give me the problem above!). Below those settings is a list of Host Interfaces, in which "eth0" appears (the only one).
Do I need to add something in /etc/network/interfaces? Or is there an option on the core I need to change in admin? Why on Earth would it work once, and not again?!
Any help would be much appreciated.