I am going to be running a webapp  on a VirtualBox virtual machine, and I want to be able to access it (via a browser) from the host, and from another machine on the same network. (That is, on the host browser I type in 18.104.22.168:3000 and get the webapp, on the remote browser I type in 22.214.171.124:3000 and get the webapp. No need to access the webapp on the VM itself.)
The ideal setup will be Windows 7 host, Ubuntu Server 10.04 VM, and I want to access the app over the network from an Ubuntu 10.04 machine.
Only if this is impossible, I'll swop them and run an Ubuntu 10.04 host, Ubuntu Server 10.04 VM, and access the app over the network from the Windows 7 machine.
What VirtualBox settings do I need to enable to make this happen? What settings do I need to enable on the host to make remote access to the VM possible? (NB, Windows 7 host ideal, Ubuntu host only if this is impossible.)
 Mesabe, the private open-source version of Wesabe, a personal finance tool. Code at http://wiki.github.com/wesabe/mesabe/ and installation script at github.com/nylen/openwesabe-installer
I've already found serverfault.com/questions/136715/how-do-i-access-a-web-server-on-a-virtualbox-from-the-host-machine which answers the host-VM part of the question.