a) which Ubuntu are you running? It matters.
b) which Windows are you runnnig? It matters.
c) I use bridged network connections. Then the host and client see each other as network peers. A server will need a static IP, so after installation, set that up - dont leave it with DHCP. This removes all the fancy tunneling that isnt needed. Remove all VB forwards.
d) Did you allow the windows firewall access to the guest VM?
Virtualbox is fine for developers, but if you want to run a real server, look into server virtualization. It is faster, more stable and more like the real server you will use at deployment.
is the command that works on 12.04 LTS. Notice the exact spelling - if you use tab-completion, there shouldnt be any question, but it is impossible to tell in a forum post if you did or just mistyped it here.
sudo /etc/init.d/networking restart
If you are running a server, THAT is the version you should be on. Servers = LTS releases. See my signature for more about that.
Besides that Charles knows his stuff. A reply that you have tried these things would be appreciate.