I recommend using the Hyper-V management console to manage your virtual machine. I haven't had the privilege of using Windows 8 Hyper-V, but I manage a couple of Hyper-V servers. You can download the Windows 8 RSAT tools from Microsoft, which comes with the Hyper V management console. Once you have that installed point it to your localhost.
Now, make sure you external network is set to the proper network card of your hyper-v server. In my example my external network is connected to the gigabit ethernet nic of my physical machine. To get to this menu, right click on your hyper v server from the management console, and select 'Virtual Network Manager'.
After that, for your VM settings, select the same Network that you configured for external access in the previous step.
And last (or first?) make sure That the physical computer has access to the network.