If your system reports that it's using VMware hardware, than we can guess that you are running Fedora 18 in a virtual machine. Correct?
For a VMware virtual machine to be able to do desktop effects (including the desktop cube), the *host* machine needs to have proper 3D accelerated graphics installed and working. For example, if you were running VMware on a host machine that was itself running (say) Ubuntu, then unless you'd got desktop effects working in the *physical* Ubuntu installation, you would not be able to get a virtual machine running on it to do desktop effects.
So, what's your host operating system? And what are the desktop graphics like in it? Are desktop effects working on it?
In my experience, even though VMware has an option to allow a virtual machine to do 'Accelerate 3D Graphics' (under Settings -> Display when the VM has been highlighted and right-clicked), it seldom works for guests properly. Windows VMs, even on my Fedora 18 laptop that does have 3D acceleration working properly, for example, are never able to do Aero graphics and always return a graphics score of 1 (or don't allow an experience index to be calculated in the first place).