Comment 1 for bug 437622

The SE screensavers require accelerated graphics, which usually means using the proprietary drivers for your video card. i.e. selecting the appropriate driver from the System->Administration->Hardware Drivers dialogue.

However, as you are using VBox, I very much doubt that accelerated graphics will work.

If you really want the screensavers, then I suggest doing a native install and running with the proprietary drivers.