Virtualbox port fowarding

[gewitty]

I have a web server running as part of a LAMP stack on Virtualbox. Everything works OK and I can access the server from any machine inside my network.

I am using DYNDNS, which routes all HTTP request to my host machine. However, when a request comes in it gets routed to port 80, which is already used by my Thomson router, so all that appears is the log in screen for that router.

How do I set up port forwarding so that the requests are directed to the Virtualbox web server, which apparently also uses port 80?