I have an XP laptop on which I am running an Ubuntu distro inside VirtualBox which is running a website via Tomcat. When I am in the VM I can access the site with localhost:8080
The following helped me after a new VM and tomcat installation.
Get the IP address of the Guest OS and the port number on which tomcat was started. Then you can access it via:
IP:Port/
In case you are not able to access it still or if you get no response, try
sudo iptables -F
This would flush the tables and would reflect the new mapping. You would need to do this only once though.