There was basic 3D support for Windows guests in Virtualbox 2.1 but users using Virtualbox to run Linux guests were mostly confined to the 2D graphics driver.
What this means is that the graphics driver used inside the guest virtual machines was only capable of simple 2D graphics and thus interfaces like Compiz on Linux and Aero on Vista were not useable. One thing which VirtualBox was missing till some time back was support for 3D acceleration for guest operating systems. Make Tech Easier has extensively covered VirtualBox a couple of times earlier and we are great fans of this cross platform, open source application. Virtualbox is an excellent application to have if you’re looking to try out new operating systems and/or are generally interested in virtualisation for the many benefits it offers.
