VirtualBox, from what I have seen, is for desktop virtualization (running Linux inside your Windows computer).
VMWare has about a dozen different products which range from desktop virtualization (Player or Workstation) to creating and coordinating dozens of virtual appliances on top-end server hardware (ESX Server/ Infrastructure).
What product is right for you depends on what you want to do with it. You can always install them and try them out. VirtualBox is free (though there is some functionality left out of the free version:
see here), as is VMWare Player and Server and other VMWare products (Workstation) have free trials.
