That you would have to manually install due to licensing issues with the owners of virtualbox. That is called the PUEL (personal end user license, I think) whereas the version in the repos is the OSE edition. I have installed the PUEL edition in the past and it installed and runs great. However, the official word is to not install anything from outside of the repositories or your forum support will be reduced, which I understand why.
May I ask what you need USB for? If it is for a printer or scanner then okay, but if you only wish to use a flash drive, usb drive, or something similar, then you can mount the host /media/ folder as a shared folder, then everything mounted on the host would be readable and writable.
If you must use something from outside the repositories, then you may want to install pclos again in another partition and call it a "testing" install. That's what I did some time back, but now I just use the OSE (open source edition.)