How can I get Compiz to work in a VirtualBox VM
Solution 1:
In the VM configuration, go to the "Display" section, in the "Video" tab make sure "Enable 3D acceleration" is checked.
After installing Ubuntu inside the VM and starting it for the first time, install the 3 packages that start with virtualbox-ose-guest- inside the VM, then reboot Ubuntu inside the VM. (BTW: you don't want the package named virtualbox-guest-additions.)
If I do that, I can run Compiz without problems (Unity doesn't work though!).