I have a need to run XP on an Atom-based Netbook w/2GB of RAM. Currently I have Ubuntu 12.04 as the host OS, but would like to experiment with a lighter weight host OS that will boot more quickly. My XP virtual machine runs acceptably under the Ubuntu 12.04 host. This is a single purpose set up that I potentially would like to redistribute to some other members of my team. I'm not married to Virtualbox, but would like to leverage an already constructed Virtualbox machine set up if possible.
How much lighter do you want to get? I running Ubuntu Server 12.04 and that is pretty light weight. I am running Virtualbox inside that build which run another Windows Server and Ubuntu server for testing new builds. I was doing this all on an old Celeron CPU which was working just fine. Not sure what you question is but I think Ubuntu is a great option for you.