If you need assistance, you'll also need to describe if the host is expected to perform other tasks.
- Assuming the Windows machine is the host, it's also a normal Windows client, correct?
- Where is the physical WAN connection?
- Where is the physical LAN connection?
- Are these interfaces bridged to real PHYs on the host?
- Are you assuming that your Windows device will get an IP via DHCP from a router it's virtually hosting (that won't work)?
If the last question is true, this thread may help:
(Hint: for the host, you'll need to static assign the IP on an Internal/host only Interface - ignore the VirtualBox network config it creates.)
It's optional to keep unless user wants to bridge more PHYs for LAN or a passed-thru WiFi card.