The VM from Musicbrainz comes as a console only install. Unless your familiar with X11, your best bet is probably something like:
sudo apt-get install ubuntu-desktop
This will install a lot of packages, but will come with a default configuration that should work out of the box.
If all you want to do is forward a couple X windows to your local machine, something like:
sudo apt-get install xauth
sudo apt-get install xeyes
export DISPLAY=192.168.1.108:0.0
xeyes
Should pop a gui window on the machine at 192.168.1.108. Substitute your ip/hostname, and an application more useful than xeyes 
However, this will invariably require some configuration on your part (setting up X on your Mac, tweaking X settings on the server, some other annoyance).
More info can be found here:
https://help.ubuntu.com/community/ServerGUI
Hope that helps Paul!
-The Ourea