Warning: unknown version of the X Window System installed. Not installing
X Window System drivers.
One possible explanation to this is that the 2.1.4 vbox video drivers do not yet support Xorg version which ships with Alpha 6. However, I found that according to this post viewtopic.php?f=3&t=12415&start=15 , 2.1.4 vbox video drivers should work with Xorg 1.6RC. Sadly it seems Alpha 6 ships with the final verison of Xserver 1.6 which was released on feb. 25., a week and two days after VBox 2.1.4 release.
Anybody experiencing the same issue? I may be mistaking.