virtualbox.org

Here's what I'm attempting to do. It's pretty complex so I'll try to keep the description simple and concise.

The goal is to connect to a network attached TV tuner through a VPN connection from a Win 8 Enterprise hosted VirtualBox Win 7 Media Center guest.

The Windows Media Center has to be a VM because the host has to be Win 8 Enterprise which has no mechanism for installing Media Center.

Host to have OpenVPN connection to the LAN with network attached CableCard TV tuner.

Can the guest use the hosts' OpenVPN connection or will the guest need it's own OpenVPN connection?

I didn't follow the whole setup but one thing is for sure and answered your question : the guest will need its own OpenVPN connection.