VirtualBox provides several networking modes for attaching guests to the host machine. The default is NAT which by default does not expose the guest to the host. Check out which mode you are using by going to the settings window for your VM and clicking on the network tab. You'll see the
Attached: property followed by a drop box.
If you're using the NAT mode we can use port forwarding to expose port 80 on the guest. Open the
Advanced section on the networking settings window and click the
Port Forwarding button. On the resulting dialogue we want to add an entry. Let's name it
Web, the protocol will be
TCP the host port can be any port you want to connect to on your windows box. Let's make it
80. The guest port needs to be
80 as that's what your web server is listening to on your linux guest VM. The Host IP and Guest IP can be left blank. Click
OK for the dialogue and the setting window. Start up your VM and you should be able to connect to http://localhost from your windows machine.
For more information about how VirtualBox handles networking check out the documentation at http://www.virtualbox.org/manual/ch06.html