Of course, the GUI configuration is rather straightforward, too.

I'm sure that there's a convenient shell command that could be used for adding the port forwarding rule with VBoxManage, alternately. So, having determined the IP address on the Windows side of the adapter, then one may run the VirtualBox Qt GUI, to add a port forwarding rule for the same virtual appliance in Virtualbox. Of course, the Virtualbox virtual appliance should not be running when the address is changed, or Windows might not correctly propagate the address change for that interface. If should the IP address collide with other network devices, the IP address can be changed, via the 'Properties' window - as available from the same 'Status' window - then selecting the IPv4 item, and the 'Properties' button, then entering a different IP address. In the resulting 'Status' window, then after selecting the 'Details' button, the IPv4 address for the Virtualbox host-only network interface - on the Microsoft windows side of the interface - will be displayed in that status window. That address may be determined in the Windows Explorer shell, via the *Network and Sharing Center' window, in which one would 'click' on the _Virtualbox Host-Only Network adapter_. Using the NAT adapter, this configuration requires the IP address of that adapter, on the Microsoft Windows side.

For other network interface adapaters, the configuration might differ. This solution was made with a VirtualBox virtual appliance publishing a NAT type network interface adapter to the host OS.

Though my reply is a little belated, maybe it'll be of help. The Guest OS I'm using is Kubuntu, but of course the configuration between each of XMing, PuTTY, and Virtualbox would be similar. Similarly, I'm running Virtualbox on a Microsoft Windows Host OS. I was encountering a similar issue, this evening.

Xming $display