Try PC --> More Applications --> Emulators --> Get Oracle VM VirtualBox - VirtualBox Installer. And that is how I got here. See the thread below this one. http://www.pclinuxos.com/forum/index.php/topic,108602.0.html
I really don't know what to say about your not being able to install an OS. I have numerous VM installations that installed without any issues. I even installed VBox in a VM, just to see what that might be like, and what limitations would be imposed. (You can't get a GUI desktop)
VMs installed with earlier VBox versions prompt to install the newest guest additions when booted, which is only a three click deal.
How much physical RAM do you have on the host machine, and how much are you allocating for the VM? Have you ever run memtest on your RAM? Faulty RAM, or not enough, would be my first suspects.